Initially, when you have a few people you know really well and get on with, you can post quite freely knowing that it's unlikely to come back and bite you.
Later, as you gain a truckload of acquaintances you have to be much more measured and it winds up feeling like you're running some sort of discount PR agency.
Perhaps Metcalfe's Law applies up to a certain size, and then tails off thereafter.
There is a limit on the number of people that us humans can reasonably be expected to have friendships with. I have a feeling that it is substantially smaller than the number of 'friends' that facebook attracts.
The friendship limit you speak of has been hypothesized by an anthropologist (Robin Dunbar) as being in direct correlation to neocortex size. More recently, it's been called "the monkeysphere".
One can't live like this for too long, you have to be yourself instead of a filtered, cleaned-up politically correct version of yourself.