There always seems to be something affecting your SEO rankings. Most recently, people have had issues with personalized search. Another kink in the chain may be social search.
The first thing is that Social Search can’t replace Hyptertext search (such as Google/Yahoo!/Bing/etc). Social search has 3 inherent drawbacks, time to receive information, credibility of the source, and subject/objectivity. Technically subjectivity is an issue with hypertext searches as well, but since the information is considered more permanent, people tend to be a little less opinionated and a little more objective (if the information is factual).
According to a recent NY Times article, the majority of social searches are answered within 10 minutes. In our culture, 10 minutes is a long time to wait. We are all about instant gratification. With regard to credibility, most of the time social searches are requests for opinions, so credibility isn’t an issue. What one thinks of a restaurant or some other establishment is generally an opinion based question.
Ultimately I don’t believe there will be a direct impact on SEO. Social search just aim to fill a different niche. People have a different goal in mind when performing a social search than when they are performing a non-social (hypertext) search.
The one thing that this article in the times neglected to mention is that a lot of the hypertext search results are becoming social. With the hypertext search engines indexing sites like Yelp and TripAdvisor for example, they are already allow social search results in a hypertext search engine. Therefore social search engines will need a wholly different approach to searching to be effective.