I have a general rule that I don't play computer games that require moving with the keyboard/mouse (which basically rules out all FPS/TPS/etc games. No big loss.) so for the most part, none. However, if presented with the choice (like in a racing minigame or something), I go for the arrow keys every time. Moving with letters feels too weird, and I'm right-handed, so it feels a bit more natural to manoeuvre with my right hand. I'm fine with steering left-handed if I'm using my thumb (PS2, DS etc) but actually pushing different buttons with my fingers? Hehe, nah.
Of course, this presents me with a dilemma when faced with a game like, say, Borderlands, where you turn and shoot with the mouse, but move with the keys. There is no way I'd be able to operate a mouse with my left hand, so . . . yeah, I just don't play those kinds of games. I much prefer console games anyway.