Depends on the game. For Aion I used it for the F keys. For Guild Wars for the 6-0 keys. Runescape I use it as push to talk for ventrilo (cuz runescape wont let me use the F keys on it).
I use a Microsoft Sidewinder x5 (wired). Fantastic mouse, fits my hand great, and doesn't show wear after ~2-3 years of daily use. But yea, I don't use the extra buttons.
