These days, you can’t have an SEO strategy that doesn’t have social media at the core, not a good one at least. The two are merging. Dynamic SEO is king and the social search movement is tying search to your social network so tightly, not a single person will have the same results.
This graphic is a nice look at the cycle of social and search, although we would go one step further and say social is SEO and SEO is social.