If you have not heard yet, there was a study coproduced by Comscore and Group M about social media and paid search.

http://www.scribd.com/doc/20703026/The-Influenced-Social-Media-Search-and-the-Interplay-of-Consideration-and-Consumption

Above is the 6 page link.

Basically it found that social media increases visitors consumption on context, experience, and increases click through rate.

I would say that while businesses can have social media tactics in terms of using social media for specific reasons, social media is at its best and most powerful as a deliverer and disseminator of content. So yes it is a fabric rather than simply a tactic.