backdraft7 - 6:06 am on May 25, 2012 (gmt 0)
I also lost rank when adding dedicated facebook buttons. I removed them and the pages improved. The ADDThis button that includes FB AND G+ seems to be OK, but I've still lost over 6,000 search terms, so I may try to remove it too to see if things clear up. I suspect just adding G+ by itself would help. If that's the case, I'd be thoroughly disgusted.
Not sure why some sites are experiencing this, maybe it's Google's way of telling you that you better start using G+ instead of FB.