I've had one for a couple of years, it's a nice mouse but due to the fact that it's ambidextrous the thumb mounted side buttons can give you problems at times when gaming. If your right handed the thumb buttons on the left are fine, but the ones on the right side occasionally get activate due to the way I grip the mouse and vice versa if you're left handed. You can either disable those side buttons if you have the same issue as me, or you can just pop them off and replace them with the blanking plates that the mouse ships with or just disable them via the Logitech software. It doesn't happen all the time, but it does for me with rapid movement / games.
sigh. i would have just bought it yesterday wouldn't I :D
I have a few logi mice including this one and I have to say it's decent. The shape is particularly useful allowing to be used either left or right handed. I will say however the mouse to be feels quite large but then again I do have small hand's.