OS X Lion 10.7 has now been superseded by OS X 10.8 Mountain Lion. Lion, coming just 18 months after the release of Snow Leopard OS X 10.6, was the first OS X to bring the Mac closer to the iPhone's and iPad's iOS operating system, making full use of Trackpads and gestures to use your Mac.
If you're still using OS X 10.6 Snow Leopard don't forget to - some older applications simply won't work on OS X Lion due to Apple's decision to drop Rosetta support. This means you will have problems running applications like Quicken 2007, Microsoft Office 2008 and other apps which supported Power PC Macs - PPC support is gone forever in OS X Lion. According to Apple, OS X Lion comes with more than 250 improvements and new features although many of these are minor tweaks. The biggest change however is far closer integration with iOS, the operating system of the iPhone and iPad. To take advantage of the many new finger gestures to navigate OS X however, ideally you'll need either a MacBook Pro with Magic Trackpad or an external Trackpad (around $69) although a Magic Mouse will also suffice.
For those used to using an iPad and iPhone, the OS X Lion gestures will come more naturally but for others, there will be some learning to do, although there are some excellent video tutorials included in the new Trackpad preferences pane. While some will no doubt love the new way of navigating OS X, others may not want their Mac turned into one big phone or iPad - in which case you can always still use the mouse as normal. The other major change in OS X Lion is that you can only upgrade via the Mac App Store.
There's no installation DVD as with previous versions of OS X. This obviously means that you won't have a recovery disk if something goes wrong with OS X Lion, but OS X Lion creates its own 'Recovery HD' partition which, while taking up valuable disk space, means that reinstalling should be easy enough. The most important new features in OS X Lion can be summarized as: Multi-Touch Gestures: Thanks to the MacBook Pro Touchpad, the Magic Trackpad and the Magic Mouse, you can perform actions using various finger movements in OS X Lion. Launchpad and Mission Control: Get a convenient overview of your open windows and applications in OS X Lion's Mission Control and access/organize applications much quicker with Launchpad. This provides a more iPhone like way of accessing apps as an alternative to using the Dock but unfortunately, unlike the Dock there's no way of seeing which apps are open and which aren't. Full Screen Apps All of your applications can now take advantage of full screen mode in Mac OS X Lion. This is something that Windows users have enjoyed for years and means that users can finally use their apps without any background distractions from OS X.