Social media marketing can work well if it's well targeted. Teen/music sites (Myspace) or technical and internet sites (digg/shoutwire/slashdot) work well. I've seen too many peole just trying to spam any old site and then complaining that it doesn't work. I've actually received MySpace bulletins from a guy selling furniture, would he really be surprised that the 16-25 demographic isn't interested in what he's selling and are pissed off with his spamming? The secret is to keep things targeted, don't spam nad be patient, as with any marketing it takes time.