I in no way judge anyone's parenting- what you do with your kids is your business (barring, you know, abuse and such :P). I'm not saying I won't let them on the internet, I just won't allow them individual access to social networking sites- most of which, for as long as I checked, banned you if you weren't 13 anyway. Personally, I'd rather take the lazy-safe approach of not having to monitor anything, rather than feeling like I had to have strict protocols and stuff.
When I grew up, my computer was in our dining room where my mom could check up on us all the time. It didn't move downstairs to the basement til I was 10 or so, then moved up to the landing by my room when I was 13. At which point we could each go on at 1 hr intervals. I think my mum did ok by us..