Don't waste your money
This is a piece of junk.
Don't get me wrong, the design is great- it was one of the few with a back button, which is very handy.
However, I've had it for maybe three months, and the thing has already burned its way through two AA batteries. a Microsoft salesperson talked me into buying it, and boy do I regret it. 'Oh, I haven't had to change my battery in a whole year!' Sure, whatever.
What a waste of money.
I've found that the 'BlueTrack' actually works worse than a regular optical mouse. I had to turn the tracking speed up to the maximum to get it to notice that I was actually moving the mouse.
Not to mention the fact that the software likes to randomly decide: I'm not a Microsoft Mobile 4000 Wireless BlueTrack Mouse, I'm something completely different! Ugh.