muzza64 - 4:49 pm on Sep 17, 2012 (gmt 0)
I think with the non-Google social stuff it all boils down to how social activity affects your user metrics (user engagement).
I don't think Google cares how many times people have liked or tweeted your site, or whether you're a 'social authority', I think they care about how engaged visitors are when they come to your site, relative to other similar sites/pages.
User engagement has a lot to do with how much people trust your site and trust is made up of numerous different factors like have I heard of the site before, is it nice/easy to use, do I know anyone who uses it, is it fast, plus a million other things we subconsciously take into account in less than a second.
Activity on social networks influences trust factors. I know who in my group of friends I can trust to recommend something good and I'm likely to give a site more of a chance if they recommended it than perhaps I would have done otherwise (better user engagement with the site because of the trusted recommendation). On the other hand, if someone I don't know well recommends something I may check it out but with less confidence (user engagement then relies more on the site's own merits).
Also, when I visit a site that has 20,000 likes or tweets, I see that as a possible signal that the site is quite major, popular and perhaps it can be trusted, or maybe it should be investigated a bit more as lots of people appear to like it for some reason (marginally better user engagement). If the site has a low number of likes/tweets it can make me more cautious (is it a new site, or do people just not like it much).
Their influence on how engaged I become with a site all depends on all the other signals I subconsciously consider at the same time. Google can't tell which factors I was influenced by most, but it can tell whether my experience was good.
However, with Google+ they can decide whether to include certain social signals into the algo. If certain factors gain some ranking influence and you do all the right things it could potentially be more beneficial to your rankings than the same effort in Facebook. However, if people try to game Google+ (which of course they will if it's proven to influence rankings more significantly than other social networks), we might see another zoo animal to demote sites involved in undesirable activity.