I love how the "very fast" page shows some games icons and "lots of fun" is MS Office

Perhaps if several social sites offer targeted ads with the same level of precision it may decrease the ads' prices since the ads budget won't grow accordingly ? (then it would mean that people are using several services at the same time and not migrating from one to another)

http://influencenetworks.org/ may be close to what you talk about:

"Influence Networks is an open-source, collaborative directory of relationships between people, institutions and companies. Each relation has its own level of trustworthiness, so that facts can be distinguished from noise."