We used the kitchen for a computer room
(Phila suburbs, PA)
My children range in age from toddlers to early teens. The older ones learned a lot about using the computer by instant messaging with their class mates. It was amazing to watch as they chatted with 5, 6, or more kids at the same time.
The younger ones learned from watching, too. By age 5, one of my little girls was able to put a cd in and start the computer all by herself.
With only one computer, they had to learn to take turns and it took some supervising to even it it out for them. But we kept the computer in between our kitchen and dining area so it was pretty easy to see what they were doing.
The teeners are aware of the bad stuff and we remind them to be very careful when they get email and go to the chat rooms.
They know not to tell private stuff to strangers.