[Coriolis]

Sorry magoo, I tried for a couple days to use E for forward, but it totally threw off my entire left hand. That extra forced pivot point restricted the motion of my other fingers, plus it eliminated the easy use of the middle finger for weapon selection. In slow-paced games it may be fine to have forward on the keyboard, but in fast games like Q3 where you are almost always going forward, especially when you are doing lots of other keys, it's better to have it where it's unobtrusive. Forward on the mouse is just a little extra pressure on that one finger while holding the mouse; forward on the keyboard makes reaching the other keys awkward.

Just my 5 cents worth (silly inflation)