Should my family share my Apple ID or create individual Apple IDs?

I have a family iMac and an iPhone with a single Apple ID. My young son just got a iTouch and I'm trying to decide whether to create a new Apple ID for him or share my Apple ID? Can we Facetime each other on our devices with the same Apple ID? Can we play games (via Game Center) against each other with the same Apple ID? Interested in the pros and cons on sharing Apple ID or just getting everybody their own.

Thanks!