If you are considering buying the new Apple Mighty Mouse, you should check out this in-depth review by AppleInsider.
The bottom line is they rated it 4/5 “very good”.
Pros: Lightweight, precise, and easy to use. Saves time. Fantastic scroll ball feature. Simple install. It’s made by Apple.
Cons: The overall size of the mouse is a bit large. Side buttons poorly positioned. No apparent way to open and clean mouse if scroll ball becomes dirty.
One other point they mention is the software that came with it required a whopping 150MB of drive space. That’s a little hefty for a mouse.