Google’s +1s do not have a direct effect on a site’s ranking in search results. Google’s Matt Cutts said as much in a “Power Searching With Google” hangout on Google+ (via Alex Graves)
Here’s more of what Cutts had to say in the hangout: “In the short term, we’re still going to have to study and see how good the signal is, so right now, there’s not really a direct effect where if you have a lot of +1s, you’ll rank higher.
But there are things like, we have an authorship proposal, where you can use nice standards to markup your webpage, and you’ll actually see a picture of the author right there, and it turns out that if you see a picture of the author, sometimes you’ll have higher click through, and people will say, ‘oh, that looks like a trusted resource.’
So there are ways that you can participate and sort of get ready for the longer term trend of getting to know not just that something was said, but who said it and how reputable they were.”