I would say it's very over rated. There is little evidence anyone is using it to much good effect. If you look at a lot of the sucess stories, they are very much out of the user's control, for example Wispa, it was only after some users setup a facebook group to bring it back that they did - it was not planned by Cadbury etc.
Social Network is very much about what is says on the tin. People are there to chat, catchup, and their visit has a purpose - it's not lazy browsing time, it full on catch up on goss time.
Relate it to real life... your on holiday...
Facebook is you talking to all your mates, catching up on the news and gossip. A guy comes up and tries to sell you a handbag, u tell him to go away, not interested, not got any money and stop hassling u all.
Google is you in a market trying to find a handbag, u see some shops all selling handbags and one of the shop keeps holds up what you ar elookng for - u all pile into his shop and look around....
Who is more likely to sell a handbag?
here ends today's lesson lol
hope it helps
"if in doubt - paddle out"