http://techstopmuse.blogspot.com/2010/12/google-1-unraveling...
gist of it is, its their own way of entering the social graph/search space and their way of telling facebook to stay off their space.
I highly doubt this will be a generic button to share to your other social networks; that would be a poor product choice from their perspective.
By the way, just to point out one thing, I'm not entirely sure either task, FB iterating into full on search and Google entering the social market is simpler than the other. But yes Google already has its very firm foothold in search. But then again you might not be considering that Bing could easily partner up with FB is the past trends are anything to go by. In which case Google should be doing there best to come up with something special.
And question. Why exactly would it be a poor product choice? I'm basing my thinking on the design of rockmelt, it has the share button and the friend edges which basically let you watch your twitter feeds and chat with fb friends from the browser. I hid the friend edges when demoing the software, wanted to save it for the final blow. I tell you I could have left with the share button and they would have thought it was a pretty neat idea.
That is obviously not a majority vote but it might be an indicator that the share button is cooler than we think. Although yes. With all the hype that was surrounding Google Me... This does feel like a kick in the head.
For Google acting as a clearing house for social data is fine.. but even better, have your own social graph which, linked with search data is incredibly valuable to them.
Google have wanted their own social graph for a long time now - I don't think they would drop that lightly.