This has serious potential to backfire. What's the mainstream press going to do if it's obvious that you have to have a google+ button in order to rank? I'm not putting a + button on my site - no way no how that I can see this happening in the current environment. But if we're forced to offer every stat for every visit to every site to Google as entry criteria in the serps? The press will have a field day.
In my country, there are substantial privacy laws. You can't give data from your website to a third party, not without clearly disclosing this information on your site. Right now, sites that use Google analytics and don't disclose this are breaking the privacy laws (pretty sure they are, I reviewed this pretty thoroughly). You're required to have a privacy statement, yet few do. I don't care because what's it to me? But if my competitors are outranking me with +! buttons AND not disclosing that they're providing all their visitor information to Google, well now the privacy commissioner might get a call. So there's another way this can backfire. You want a call from your country's privacy regulators over your use of a +1 button?