xcoder, although my evidence is anecdotal, I would have to say yes. besides traffic, which social is about 1/3 of my total traffic now, it causes better SE ranking. SEOmoz has a couple of articles showing the effect of FB, and Twitter social signals in SE ranking. Google has admitted they use social signals as a ranking signal. Social traffic is more likely to sign up for your mailing list, click your ads, or buy your self published books. It also gives you an authority in your niche which then opens doors for you to have your content syndicated on other higher authority sites which once again gives you natural and niche related backlinks which we all know is what Google wants.
I think that this is the natural progression of backlinks that Google wants to see. Publish Page ---> Social buzz and signals ----> backlinks from other sites = quality content.
Just this weekend I saw this process in action. I published a niche related article. It received 416 social signals between FB, Twitter, Pinterest, and G+. Within a couple of days it received backlinks from 2 Paper.li papers, 3 forums, 1 niche related bookmarking site, and 1 blog. The reason I know this is because I received traffic from all of those places. Not one of these links were built by me. They were all 100% natural and came all of a result of focusing on social networking.