I like to think that I'm reasonably well adjusted as a person (stop sniggering at the back there). By this I mean, I know the difference between violence depicted on pixels and real life. Reading about the Georgian teens who apparently learned how to make Molotov cocktails via GTA made me just want to dig Liberty City Stories out again.
And that's the difference. I'm intelligent enough to know what's real (e.g. Buffy) and what's not (e.g. Terminator) and know what's right and wrong. I play on GTA a fair bit, yet don't get the urge to gun down swathes of pedestrians (well, no more than normal people). I play on Settlers way too much, especially while off sick, yet have never sent a battalion of Roman troops in to attack a Chinese guard tower. I play on Quake, yet I'm a crap shot. I should comfortably be able to say, hand on heart, that computer games don't effect me.
Until I hear the opening riff of Sweet Child O' Mine on Planet Rock, and suddenly my mind thinks "Green blue red green orange red blue red green blue red green". Maybe I'm not as well adjusted as I thought.