I hated the Mighty Mouse and had high hopes for the Magic Mouse.
The shape of the mouse is pretty horrible - it's beautiful to look at but very flat and hard to hold well - it doesn't fit your hand at all. As with many Apple devices this is a triumph of form over function and as with other Apple mice especially it's over engineered. There are lots of great mice out there that CAN click both buttons together and that work with Bluetooth. In trying to make a better mouse Apple constantly introduces limitations that are annoying and unnecessary.
Agreed that the shape isn't particularly ergonomic, I'm worried it will encourage RSI.