Google has added tracking for the +1 button in Analytics reporting tools. Elements such as Facebook likes, +1's, and other user web endorsements are quickly becoming the trick that makes pages rank higher in organic search results. Every time a user clicks the +1 button or likes something, they are publicly endorsing that page, image, or other content and letting their entire network see it.
Now website can track the +1 clicks in Analytics. In Google Webmaster tools you can see how traffic is affected by the button. For instance you can see if users stayed on your site longer in correlation with clicking the button. Traffic that has clicked the +1 button is denoted by a +1 annotation in reports. A separate activity report shows how many times the +1 button was clicked on your own site and on other sites as well as in Google search results pages or other SERP's.
Many of the metrics that are already on Analytics such as geographic and content data are also applied to the +1 metric. This would be a great tool for identifying content that users like which is a large determinant of time on site. Now there is a way to track exactly what content visitors are finding appealing so that is can be spread around to other areas of a site or enhanced in order to make pages more sticky.
You can read more about +1 tracking on the Adsense Blog.