deadsea - 2:15 pm on May 22, 2012 (gmt 0)
Does WMT report that +1 in the SERPS had a negative effect on the click through rate?
I have a friend that reports that WMT reports lower CTR for his site too when SERPs are annotated with +1. His theory is that Google is showing your site in some case in which it otherwise wouldn't because a friend of the searcher has done a +1 on your site. He thinks that because of this increased exposure, you are showing up for less relevant terms and the CTR is lower.