It seems to me that more and more companies are using social networking sites, especially Facebook to do marketing. Personally I had some groups on Facebook that is somehow related to some of my websites, however I never really did any promotion on my websites other than putting the link on the group.
Prior to facebook, I do have some account on Friendster that targets towards a geographical location. This is because I was poor and had to utilize every Internet marketing technique I can do that will not cost me money, this was one of the method used. I would post some updates on the bulletin. I believe that it does bring some users, however I am unable to track them.
One obvious observation is to when my friends started organizing an events at Facebook to his restaurant’s Grand Opening at Jaya 1. More than 200+ people turned up to his restaurant opening. And the opening ceremony did pretty well, with people flooding the restuarant. Plus it is quite easy to invites friends that are not so close to you and you are shy to call them one by one.