I think there's a crucial distinction to be drawn between games changing what you do, and them changing how you do it. I think the latter is far more likely than the former.

If I'm used to driving at 200 mph from playing Burnout, I can see how that might affect my driving in real life - it's a case of muscle memory and reflex - but playing Burnout doesn't induce me to jump in the car and go for a drive. Similarly, if I've been fragging people with a flak cannon in UT2K4 then arguably I may prefer to use a flak cannon when I frag people in real life. Except, of course, that I don't have access to a real flak cannon, and there's nothing about playing UT2K4 that creates a desire in me to kill people.

It's like that line in Scream: horror films don't make people into psychopaths, they make psychopaths more creative. Violent games don't make people inherently violent, but they may mould the precise form of the violence someone chooses to engage in.

You know how Wightfrag goes: one minute you're shouting in frustration as your power core explodes, the next you're asking if people need any help with the washing up and insisting that they have the last party ring, you're quite happy with Pringles :-D