A recent research paper that suggest that video gaming can help reduce anger and make people more relaxed has been getting a fair mount of internet publicity. Mind you another paper presented at the same conference (in my home town of Dublin) suggests that heavy gamers become like sufferers of the autistic disorder Asberger's syndrome.
I can empathise with gaming helping people to relax. I have always found an enjoyable fragging session to be a good way of winding down before bed. My wife on the other hand gets entirely wound up after a gaming session and refuses to play any game late at night.
It is a pity in that the violence research only considered World of Warcraft players. The highly stylised rule based combat of an MMO cannot compare in terms of violence with the ruthless killing found in most FPS games.
I am replaying the single player campaign of COD4. Violence abounds of course but the level "Death From Above" still stands out as the most callous kill fest I have ever experienced in any video game. You control the weapons of flying gunship literally pouring death down onto the hapless enemies below. The casual commentary of your companions is chilling in the extreme. If you have not played the game you can see a video capture here. It is long enough to be tedious sadly but if you can - fast forward to the final jocular comment: "This is gonna be one hell of a highlight reel".