lexipixel - 10:11 pm on Feb 13, 2013 (gmt 0)
They are tied to Incoming Page Rank, Twitter, Facebook and other social media signals, Whois information, etc.
On the "web according to Google"...
Google can't crawl behind the wall of Facebook.. so that signal is limited.
Incoming Page Rank: that's a Google factor.
Twitter: as a social signal to infuse credibility on the rank of a particular web page -- that would mean that the HTML, linking and credentials were setup in just the right way for (Google) to recognize "Oh, that's from Fred, he's more trustworthy than Joe, because more credible people follow on him on Twitter"... quite a stretch.
It's all BS to push people to sign up for Google+
The sooner everyone gets off the Google Koolaide, the better.