If you can, try one out before you buy, most people I meet are evenly split down the middle on them. They're a bit odd because they're so flat and if you've been a happy mighty mouse user you'll probably dig, but if you've been using a PC style scroll mouse, stick with one of those I reckon.
For my money, I love the apple keyboards (I have one on my pc as well as for my mac) but cannot stand the might mouse or magic mouse and I like those Logitech gaming nerd mice as a substitute, they feel nice to use.
I absolutely dig my Magic Mouse. It feel so much more natural to me after using it for a bit, and I find I get less RSI rubbish with it to. Mice are pretty damn subjective though - I know a stack of people that use weird ass gaming ones or even those upside down things with the ball on the top. :|