"At the moment reputation is largely determined by the quality and ultimately quantity of back links but I believe Google are moving towards assessing whether a site should rank based on the authority of the author, how socially shared it is in addition to how well linked it is.
So if you want your website to rank you’ll need to think about how you can make progress in all three of these areas. Unless there’s a dramatic shake up in the relationship between the major social services and Google the best data they have access to is their own network, which I think justifies taking the platform seriously.
But before we get to that stage social is already heavily influencing natural search results".
Via Antonino Militello