My standard answer, and I’m talking about web search rankings, has always been that Google basically treats links the same, you know. We use the fact that you have PageRank. So, we know how reputable the site is, and so, you don’t just look at the number of links to a site. You look at how reputable those links are.
And then applies to Twitter or Facebook as well. Now, one thing that’s kind of interesting that you have to bear in mind with Twitter and Facebook, let’s start with Facebook. A lot of those profiles are not public. And Google can only assign PageRank on the outgoing links if we can fetch the page to see what the outgoing links are, and so, if you profile on Facebook it’s completely public where Google can crawl it. Then those links might flow PageRank. If we can’t fetch them then they probably cannot.
And that leads to a first approximation that’s probably a good answer for Twitter not to have to worry quite so much about Spam and people trying to just like crowd them up with all kinds of links. So while at least in our Web search, our organic rankings, we treat links the same from Twitter or Facebook, or you know, pick your favorite platform or website. Just like we treat links from WordPress or edu or gov like that.
It’s not like a link from an edu automatically carries more weight or a link from a gov automatically carries more weight. But the specific platforms might have issues, whether it’s not being crawled or whether it might be no follow that would keep those particular links from flowing into PageRank.
by Matt Cutts - Google's Head of Search Quality Team