Mac OS X
If you're a Windows user, it takes a little getting used to the Apple environment. The advantage of Apple is that the OS is fairly logical. Main differences include using mostly one mouse button, different shortcuts and keys and the fact that the menu of the active program is always at the top of the screen.
The MacBook Pro with Retina still comes with OS X 10.7 Lion. The next version of the OS will be released next month, and will be called Mountain Lion. The update will be free for consumers that bought the new MacBook Pro with Retina. If you don't have Apple's latest laptop, the update costs $19.99. The new version has better integration with Apple's iCloud, which lets you store documents online, and gives you access to iMessage, which lets you quickly share data via the menu bar. GameCenter, currently available on Apple's iOS devices, is also part of the new Mountain Lion.
There are too many tips and tricks in MacOS X Lion to mention here. Being able to swipe with three fingers from left to right between maximised programs is handy. It gives the feel of a multi-monitor environment on just one screen. When you swipe with two fingers, you flip between pages in for example a browser. When you swipe upwards with three fingers, you get an overview of all open programs in Mission Control. In Mission Control you can create a new desktop with only certain programs. It's quite handy when you are very busy, but you can lose the overview at times. Note, however, that this isn't something unique to Apple. Other manufacturers of touchpads, for example Logitech, also have multitouch peripheral devices.