I was wanting to use Fitt's Law to create an aiming offset for bot aiming, I guess it could be adapted to 3d environment, it's currently used for analysis in HCI on 2d planes to get probabilities of peoples ability to hit a button on a screen.
check out Fitt's Law :
http://ei.cs.vt.edu/~cs5724/g1/glance.html
I'm sure you've heard of it, ever had a look? (Just the fact it's quite well known and has been tried & tested)
Really this is what you want to use for multiplayer gaming bots, afterall we're simulating real people trying to hit a target with their crosshair on a 2d screen.