What's that in the center? It isn't quite a scrollwheel and isn't quite a trackball. It's a 360-degree scrollball that is designed to let you scroll in any direction. I'm not too much of a fan of Apple hardware, but this sure does look sleek.
Borrowing from Xerox, Apple was probably the most influential company in bringing the common mouse to the desktop. Years later they are still innovating, or at least trying to do such with style. The so-called "Mighty Mouse" is an OS X and Windows compatible device, and therefore of course includes multi-button functionality.