1) As Al mentioned, it is heavy and awkward for right clicking.
2) As with other Apple mice, Apple seems to think people enjoy having to physically pick up the mouse repeatedly to traverse the entire screen.
3) While iGesture (or whatever its called), is kind of cool, particularly the scroll function, it is rough around the edges, and not yet seamless enough that I would not like some extra buttons for flipping back and forth between web pages, etc. But god forbid we should have more than one button!