A new study seems to show that there is no relationship between violent videogames and real-life aggression. From ScienceDaily:

Writing May 14 in the International Journal of Liability and Scientific Enquiry, Patrick Kierkegaard of the University of Essex, England, suggests that there is scant scientific evidence that video games are anything but harmless and that they do not lead to real world aggression. Moreover, his research shows that previous work is biased towards the opposite conclusion.