This debate has been going on for years and years. I even had to write papers about in college and we had debates about it in one of my classes. For me, it's one of my "soap box" topics!
I won't even get started.
I agree with dukkillr that there may be a correlation but certainly no causation. I've heard many "educated" people talk about how games like Doom and GTA teach you how to aim a gun. That's ludicrous. If they've ever played these games and then shot real guns, it would be obvious to them that there is no truth to that. GTA is 3rd person...explain to me how that teaches you to look through the sights of a gun.
If anything, in my experience, I think video games can be a release of anger. I'll probably get arrested for admitting this now but, one time, I got pulled over and received a ticket that I didn't think I should have (imagine that). I went home, fired up GTA4 on the PS2, and went around the city killing every cop I could fine until I got a 5 star wanted level and the military took me out with tanks! haha.
Anyway, like I said, I won't get started. I heard a quote the other day that I really liked though..."If guns kill people, then pencils misspell words." No one seems to care that this nation is raising kids in public schools who can't spell, are told that's ok, and also told that there are no losers in anything. Wait until these kids hit the real world and find out that life is not fair, there are winners and losers, and you WILL be JUDGED on your performance. Wow, what a revelation!
Ok, I'm done...and way off topic...