Most Apple fans couldn't wait to download OS X Mountain Lion, the eighth iteration of the OS X software line for Mac, and as a result, the Mac App Store was flooded early Wednesday morning with download requests for the $19.99 upgrade.

Most early adopters of Mountain Lion already love the beast: As advertised, Mountain Lion is Apple's attempt to seamlessly blend the traditional features from the Mac OS with the wildly popular features of the iOS platform for iPhone and iPad, such as intuitive gestures and more options for sharing content, staying organized and communicating.

However, most major software upgrades are not without their fair share of bugs, issues, errors and omissions. Would OS X Mountain Lion suffer the same fate? Here's what we've learned this morning from those that have had a chance to delve into OS X Mountain Lion.

A Speed Demon, For The Most Part

The most talked-about feature of OS X Mountain Lion, among those who have already downloaded it and/or reviewed it, is the speed at which it runs. Apple probably could have called it OS X Cheetah.

Many users of the last Mac operating system, OS 10.7 Lion, experienced issues with inconsistent frame rates, slow loading times and freezing. In the few short hours of Mountain Lion's release, nearly all reports and reviews are free of these speed complaints. However, Gizmodo's Jesus Diaz discovered a few issues with his computer's speed, most interestingly while using Apple's latest laptop, the MacBook Pro with Retina Display.

I used this computer for reviewing the final version of OS X 10.8 and, while it was perfect with Lion, the display is now very buggy, Diaz wrote. The zooming is often slow, the cursors sometimes disappear, some parts of the text fields don't refresh properly in Safari, animated GIFs get garbled frequently, and videos sometimes get distortions, especially if you try to rotate them in QuickTime Player. At times, there is also a perceptible slowdown, even while this is a fully loaded system with 16GB of RAM.

Perhaps this is a problem unique to my computer, but I doubt it. None of these problems were present with the factory-installed OS X Lion. And this computer was almost virgin before the upgrade from Lion to Mountain Lion.

Apple says that Mountain Lion is compatible with a handful of Mac Models, including 2007 iMacs and later, the late-2008 aluminum MacBooks and the 2009 MacBooks, all MacBook Pros that debuted after 2007, as well as MacBook Airs and Mac Pros after 2008.

Apple has also made Mountain Lion compatible with 2009 Mac Mini models and later, as well as Xserve devices. (To find the exact model of your Mac by clicking the Apple icon in the top left corner of your computer screen, clicking About This Mac, then clicking More Info on the bottom.) We have not heard any negative reports about the speed from these older Mac users, but if you belong in this category and you're experiencing any issues with Mountain Lion related to speed clipping, let us know.

Missing Files?

Some users may discover that after upgrading to OS X Mountain Lion, some of their old files and applications may have gone missing. Of course, this is always an infuriating moment for Mac users, when they can't find what they're looking for after a major software release.

Not to fear: Apple was ready for this issue: Mountain Lion automatically identifies the applications and documents that won't work on the new OS and places them in a folder in your Finder, appropriately named Incompatible Software.

Missing Software

Mountain Lion has everything Mac users have been expecting, with the exception of one major feature. Deep integration with Facebook, which was a promised feature back in February, is nowhere to be found, even though it was included in the developer's version.

It's likely that Apple will roll out Facebook integration once iOS 6 launches this fall - that, too, promises deep integration with the social network - but Apple has not explained why the feature did not arrive with the rest of the platform. Once we get official word from the company, we'll let you know.

Incompatibility

Adopters of OS X Mountain Lion will be disappointed to learn that, in typical Apple fashion, a handful of apps won't work with the new Mac operating system. Apple Store employees may not know which applications are incompatible; luckily for us, we have RoaringApps to tell us.

To check out which of your favorite OS X and iOS applications will work with Mountain Lion (and Lion too), check out RoaringApps' full table of compatible and incompatible applications. There are literally thousands on this list, so it's best to use the search function to find which apps you need before upgrading to Mountain Lion.

For the most part, however, new Mountain Lion users don't have many complaints about incompatibility. This ought to be an issue exclusive to niche users of particular third-party programs.

Other Issues?

So far, it's still very early in the game to be hearing about major software issues with Mountain Lion; many users have yet to install the program, and the next wave of installments won't likely occur until later today when 9-5 employees return home to their Macs.

We ought to be hearing about more bugs and issues with Mountain Lion over the next few days, as Mac users get a chance to download and fully explore the 200+ new features in 10.8. Cautious users may want to wait before upgrading to Mountain Lion, but for users that can't wait, this big cat has a lot to offer.

Here are some of the features to look for in Mountain Lion.

Notable Features in OS X Mountain Lion

Messages: In iOS 5, Apple dumped SMS text messaging on the iPhone and iPad and replaced it with a free platform called iMessage, a BlackBerry Messenger-type service that allowed Apple users to freely message each other text, photos, and videos to and from any iPhone, iPad and iPod Touch.

Messages is essentially iMessage for the Mac. It lets one send free and unlimited text messages from a Mac to anyone on an iPhone, iPad, iPod Touch, or on another Mac, letting users continue their conversations on any Apple device. As with iMessage, users can also send rich text, photos, contacts, locations, and even 1080p HD video to their friends. Furthermore, Messages supports FaceTime -- along with other instant messaging systems like AIM, Yahoo!, and Google Talk -- so users can pick up their chats no matter where they started.

Messages also comes with delivery and read receipts, encrypted messaging, and supports large attachments such as high-quality photos, full 1080p HD video, or documents up to 100 MB. Apple also makes it easy to switch from text conversations to video calls with a new FaceTime button.

Airplay Mirroring: One of the best -- yet most underrated -- features on iOS 5 was the ability to mirror whatever was on your iPad or iPhone 4S directly on a television hooked up to an Apple TV. In other words, iPad and iPhone 4S users could display high-definition movies, presentations, slideshows, photos, and websites onto a larger television screen wirelessly and seamlessly.

For those who download the OS X upgrade, let us know your thoughts! Send in your reviews and leave your impressions in the comments section below.

Notification Center: Before Apple added the Notification Center to the iPad and iPhone, new texts and app alerts interrupted whatever the user was doing by popping a message directly in the middle of the screen. The Notification Center solved this annoyance by making notifications into small bars that appeared at the top of the device's screen momentarily, and those incoming notifications also did not interrupt the user's activities.

Apple wants its users to stay up-to-date across all of their devices, which is why the company added the Notification Center to the Mac in OS X Mountain Lion. By swiping the Mac trackpad with two fingers from right to left, the Mac Notification Center appears on the right side of the screen. Notifications from apps like Messages, Game Center, Mail, Calendar, Reminders, and other downloadable third-partyapps from the Mac App Store will tell you when there's something you should see. Like the iOS Notification Center system, users can choose which apps they want alerts from, and users can easily hide the Notification Center with a simple swipe.

Twitter Integration: Apple understands that people love and rely on Twitter to engage in the greater social community, and in iOS 5, the company gave its iPhone, iPad and iPod Touch users the ability to tweet from almost any app. Users could tweet photos, links, locations and webpages effortlessly. In less than a year, this platform has become huge for both Apple and Twitter: iOS 5 users sent more than 10 billion tweets since the platform went live in October.

With OS X Mountain Lion, this deep Twitter integration has reached the Mac, giving desktop users the ability to tweet out directly from apps like Safari, Photo Booth or iPhoto. Just like iOS 5, a Tweet Sheet pops up, with a paper clip over any attached image or website, and the user can write their message, add a location if they want, and send it out from there. It's simple, clean, and fast.

Facebook Integration: After successfully baking Twitter directly into the OS software, Apple has decided to open up built-in support for Facebook. Now, after signing into their account just once, users will be able to share content -- text, links and photos -- onto their or others' Walls, automatically sync their Contacts with their profile photos from Facebook, and receive notifications over the Notification Center.

Notes: Finally, Apple created a proper notes application for the Mac. Until this point, Mac users made do with an app called Stickies, which allowed them to create virtual multi-colored sticky notes and place them all over the computer screen. This app, while fulfilling a need for notetakers, had no way to search the notes or organize them efficiently.

This has all changed in OS X Mountain Lion. The new Notes application on the Mac takes after the app with the same name on the iPhone and iPad, which lets users create and search notes in a clean and easy-to-use interface. On the Mac, however, users will also get a chance to add photos, movies and links to their notes, as well as rich text, bullet points and formatted lists. For those users that will miss Stickies, Apple also allows anyone to tear the note right out of the Notes app and stick it anywhere on their desktop for easy access.

Game Center: The iPhone, iPad, and iPod Touch were all great devices for playing cheap and attractive virtual games, but before iOS 5 came along, there was no way to track and organize your progress, especially comparing it to other customers playing the same game on their Apple devices. With the introduction of Game Center on iOS 5, Apple allowed users to create accounts, keep track of their awards and achievements in games, and even compete with friends, or find friends to compete with.

But then, Apple thought: Why should iOS have all the fun? With Game Center coming to the Mac, desktop users can play head-to-head and turn-based games against friends and competitors on any Mac or iOS device like iPhone, iPad or iPod Touch. Game Center also suggests games you might like, helps you find Game Center players from around the world to play against, and provides a leaderboard of the best players in each game.

Share Sheets: It's extremely easy to share photos or links on the iPhone or iPad. A box with an arrow appears on almost every page, which allows users to book mark pages, add them to the Reading List for later reading, mail the page to a friend, tweet it out to Twitter followers, or print out the page on a nearby printer.

In OS X Mountain Lion, Apple added the Share button to most apps within Mountain Lion, which similarly lets users add pages or links to their reading list, bookmark them on their browser, e-mail or tweet them out, or send them via Messages or iMessage. Not every sharing option applies to every page you see on the Mac, but Apple tailors sharing options based on the app you're using. For instance, some sites may allow you to share the page on Vimeo or Flickr, while others only allow Twitter. But once you perform a single sign-on for Twitter, Facebook, Flickr, or Vimeo, your Mac is ready to share any content directly from the apps that support it.

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Have you downloaded OS X Mountain Lion yet? If so, are you experiencing any issues? Shoot us an email or let us know in the comments section below.

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