Yes social networks do help in a number of ways - just doing simple search on this aspect will show the ways in which social networks are useful.
Social Network sites will give you a good back link support and business. Before starting the social networks you have to be very clear in goal of your business. That will help you to get lot of people from social network sites and also you can get a good back links. So always try to use social network sites in a multiple ways to generate traffic.
I'm not sure about backlinks from Social Networks, but we can get some considerable amount of traffic from Social networking sites.