I'm on there (thanks aDam) but I don't know if I'm going to full on convert from FB yet.
If fb is smart and implements circles I don't think they'll need to worry about google+, but if they don't well...damn those circles are bitchin.
I think it was actually aDam that posted on squirrel's that there is already something like circles in fb but whatever it is it's not as prominent in the interface as g+.