goodroi - 1:54 pm on Oct 13, 2011 (gmt 0)
rainborick covers it pretty well. Don't forget that Google recently admitted they will still crawl a page that has a +1 button even if you block it with robots.txt.
There are also some other options you can do.
#1 - Use htaccess to block all traffic from Googlebot
#2 - Use htaccess to redirect the referrals from backlinks elsewhere.