Too late. The ship has sailed on this and Google was left standing on the pier.
Just like iTunes will never be dislodged as the dominant music site, Facebook will never be knocked off its perch in the social arena. It's good enough and people are too lazy to bother learning the ins and outs of a new social website, much less go through the agony of porting all their personal content.
I love the Circles feature though, but guess what, Facebook will just copy it.