Just thought I'd share my thoughts on this matter.
Its a much debated and very intriguing theory that somebody who watches something violent would be moved for whatever reasons to go and recreate that act themselves on another person.
Myself, I think that this may be partly true in some ways, but "videogames hurt our children" is a steaming pile of MerkinMedia paranoia orgyfest.
I am an avid gamer and I always have been. Being a manly man, I usually prefer the ones where I get to mow down (or slice up) countless waves of feeble bad guys with my teh uber awesome nucular chainsaw deathgun. (read: GOW2, Fallout3, R63, doom et al)
However, I have only once violently attacked another person. I was 12, and he started it.
Also, at that time the worst kind of violent media I had been exposed to was Robocop, and I didn't try to blow this guy's kneecaps off with an automatic pistol before cuffing the twat and reading him his rights. Monkey see monkey do applies more to monkies than humans in this case.
If we are going to ask "Do violent video games make people shoot their parents and shout "HEAD SHOT!" ", we may awell ask "Does educating our children about violence in world war 2 make them prone to round up Jews and gas them?"
This entire debate IMHO is nothing more than a media diorrhea feeding frenzy. Just another little thing for America to be paranoid about and safeguard their children from.
In actual fact, if you feel your child may be playing too many violent video games or you disagree with their content, there are two things you can and should do.
1. Broaden your horizons, the internet is a good place for that.
2. Take the game away if you still feel the same way.
If your 12 year old is playing Gears of War 2, that's illegal and by allowing it to happen you forfeit all rights to complain about the effect it may or may not have on him or her.
EDIT:
Forgot to address the addiction angle

Game 'addiction' sounds a bit strong.
I have been very attached to completing or carrying on a game that I am really into, and because of that if someone were to walk in and unplug my PC I would probably shout at them, plus turning off PC's when the hard drives are being written to can corrupt data and sometimes damage the drive so IMHO I would be well within my rights to do so.
It is exactly the same thing as walking up to someone who is really into a good book and simply taking it off them. Or ejecting someone's DVD from the drive right before Sauron is about to get his arse kicked and Middle Earth will be free forever.
Its *VERY* *FUCKING* *IRRITATING!!*
But in most cases I suspect it would not result in violence, unless the protagonist deliberately and repeatedly performed this type of action with intent to piss me off.
rawr.