Have you installed Apple's newest operating system upgrade?
Apple claims over 200 new features in Mountain Lion. Many of these features are system and security related. There are several that will improve useability for many of Apple's customers. Some of those features that may have a bigger impact include:
Native support for iCloud. When you install Mountain Lion, you are prompted for your iCloud information. This information is then integrated into the file system, much like Microsoft has done with SkyDrive. One of the more interesting features is the ability to automatically create folders by dragging one document on top of another, in much the same way iOS currently supports. Not only are your files visible on all of your Apple devices, but it displays the documents for that particular app you are using. Don't have an iCloud account? When you run Mountain Lion for the first time it will prompt you to create one.
iMessages. You can now send a message to anyone with an iOS 5 device, bypassing SMS or email all together. Apple has come under fire recently for SMS vulnerability, but the reality is that all SMS capable devices and carriers are vulnerable to the same spoofing threats that Apple devices are. You can read more about the vulnerability, and Apple's response to it here.
Power Nap. Now when your computer is sleeping, it's doing it with one eye open. Mountain Lion can automatically update your mail, notes, reminders and messages so that when your Mac wakes up, you'll have all of your latest information. However, this feature is ONLY supported on a Mac notebook with built-in flash storage.
Mac App Store. While not new, quite a few improvements have been made. OS X updates are available there, as Apple wants you to use the App Store for updating OS X and other installed apps. The App Store will also automatically download these updates for you. Apps can now be pushed to your Mac, no longer requiring you re-download apps to each computer.
Game Center. You can use your Apple ID to setup and personalize your gaming experience. A feature directly imported from iOS, and using that account information or your Apple ID, the Game Center lets you see what your friends are playing, invite people to play a game with you, chat in-game, and keep track of you and your friends achievements in those games. It also appears to allow you to play across platforms, meaning you can play a game of chess on your Mac against someone on their iPad.
Apple has also tightened the integration with Facebook and Twitter, made improvements to Safari, Accessibility, Auto Save, and in many other areas. If you happen to live in China, Apple has improved your experience quite a bit with updates specifically targeted and Chinese language support and Chinese Government approved search and social media outlets.
A few things of note are absent or dropped from OS X 10.8. Some of them include the option to turn off smooth scrolling, a separate search box in Safari – its now integrated into the URL bar, and no more RSS feeds in Safari (or Mail). Some people are also experiencing decreased battery life, and your battery status is no longer displayed in the menu bar. You must now click on the battery icon to see it.
For a full review of all the features in Mountain Lion, check out the Ars Technica review located here.