MSD

I don't see anythign wrong with explsing kids to mainstream entertainment technology at a young age, but if I have kids, they're going to spend a few years on Math Blasters and Astro Grover* before they graduate to Mario and Three Stooges. GTA and the like won't come until they have a firm grasp of reality and can differentiate between game violence and real-life violence. I'd estimate three years after the indroduction of paintball (~ age 12) before allowing GTA into the house.

edit: I should add that video games are a good way for kids to wind down after homework is done, and when playing out side isn't prefereable due to weather or nighttime. I also envision myself as the kind of parent who wouldn't have a problem sitting down and playing a multiplayer game with my hypothetical kids. Hopefully they won't have a problem with it, either.

*- A little-known Sesame Street-based game focusing on spelling and math, I still think it's an awesome game while drunk