Let's say that a Magic-User takes an arrow to the shoulder while gathering up the energy to fire off a Magic Missile. ("Ka-me-ha... me... OW!") Obviously, the MU doesn't get the shot off -- but what happens to the rested talent itself? Does the MU lose the use of that talent until he rests or spends 2 AP outside of battle, or can he try to use the talent again the very next round?
To clarify why, I think the fact that the action failed to begin with is probably player punishment enough. However I'm not above engaging in some rat-bastardly Bowl-feeding to make such a failure complicate things worse somehow.
I would say that some of the best moments of my OSH sessions are when I say "Ok, screw it, time to F*ck with you all," and drop a couple of M&Ms in my bowl. Get your game on!
That sounds completely reasonable, though I have to admit, when the players focus talent is interpreted, that sounds like the perfect time for me to have fun. I have said it before, do what feels right and will make the adventure better!