Just 2:
one in the living room
one in the family room
we have three kids, and they think a tv in their bedroom is a good idea, but I won't do it. While oldest ds (who is starting HS) just got a computer for homework in his bedroom, no regular internet access for him (although since we have wireless, we can get it for him when he needs it for school assignments with a password)
I guess I'm a mean mom
When the kids leave home and we once again have a guest bedroom, I'll probably put one in there.