Why am I recommending you read the resource below? As social media tactics spread to all corners of the Web, it's probably a good idea to consider surfers' social media ad interaction behavior in your site strategy. With a little tweaking and contextualization, these studies might shed some light on particular problems your specific niche/site is facing.
Resource:
Psychster is a research firm that specializes in social media and social marketing studies. Here is their PDF of their latest
social media brand/ad interaction case study.
Additional resource:
Is Twitter worthless?