Many of the neat features of the Mac OS involve the trackpad, which comes standard on the laptops and is an option for the iMac as well as the MacPro. A couple of interesting gestures to know are:
Pinch – Will zoom in and out, a feature that is not only great for photos, but also for websites with tiny print.
3 Fingers Up + Swipe – This will display all of your open windows and programs. No more searching around for that one document you had open before you got lost in Facebook, Twitter, email, etc.