Google announced the addition of +1 button data to Google Analytics and Webmaster Tools. These new metrics can show you how the +1 button actually affects the traffic to your site.
In WMT, there is a Search Impact report, which shows how +1′s affect your organic search traffic. “You can find out if your clickthrough rate changes when personalized recommendations help your content stand out,” says Google software engineer Dan Rodney. “Do this by comparing clicks and impressions on search results with and without +1 annotations. We’ll only show statistics on clickthrough rate changes when you have enough impressions for a meaningful comparison.”
An Activity report shows how many times your pages have been +1′d, from buttons on your site, as well as on other pages like Google Search.
An Audience report will show you aggregate geographic and demographic data about who is using the +1 button with your content. Google only shows this info, however, when a “significant” number of users have +1′d pages. They don’t say what number they consider “significant” to be.
Users will find a +1 Metrics menu on the side of the page, where each of these reports will be able to be found.