Yes, I do believe in Social Media for promote your sites because it helps to increase your Product Brand and drive traffic on your site as well.
Social networks are everywhere and widely used by a lot of people. That is why SMO may only help your site, no harm can be done.
It depends on what sites and how you use them. The potential for good ROI is there but the probability is for terrible ROI. Also, what are your goals? SEO, traffic or branding?
SMO is the future, since people spend more time on Facebook, than they do on all Google's websites combined...
Bojan et. al, I wrote a blog article earlier this month on this very topic. I think Facebook currently has the upper hand on Google because they have the people. And they are consuming an incredible amount of demographic and psychographic data on the people. I prophesized what they're going to do with the people and their next big step in this article: What Does Facebook Have Up Their Sleeve? http://www.tbkcreative.com/social-media/what-does-facebook-have-up-their-sleeve/ (P.S. - I checked with the forum rules and it read it was fine to post a relevant link with a summary. Let me know if I was bad and I'll correct.)
ya ...ofcourse.. SMO is the one of the latest way to promote your sites . Its a latest trend or tech in SEO. You can get a lot traffic from social networking sites like facebook , Orkut , twitter.