Heres the thread for the game engine DoF - http://blenderartists.org/forum/showthread.php?t=129693&highlight=depth+of+field
Ive messed around with the script a bit, and its very good. But i usually find that a very low value of DoF works best, otherwise it seems to intense. Just enought that u can notice it is relatively good. You dont want it to be too overwhelming, because as mentioned above its not something which really works with games yet.
The best example ive seen of DoF in games is in Crysis, when u bring up the gun to change sites etc, because ur view is focused on the gun at that moment, so it looks right.
Edit Ahhhh, Sick got in before me!