Google has launched an experimental project for its continuous improvement on search engine algorithm. It is called the "+1" (plus one) button experiment, like the Facebook's like button, it is aim to make recommendations and sharing easy, except that it is focused on search engine results, meaning, more relevancy on the site, more changes on ranking.
This will make your favorite google search results stay on top of the result and will recommend to more Google search engine users.
Once you have "+1d" (plus oned) the site in search results it is publicly published throughout the search engine, all Google search engine users that search same results as your "+1d" site, they will see you and the other that "+1d" it, maybe making the site more relevant and popular.
I think that this is just another step of Google against content farming, of course people make the decision if the site is relevant or not, it is then Google's algorithm that will calculate its ranking. This is a smart way in the first place, let people recommend to other people the most relevant site they could find and share it more easily.
How to use this new feature from Google? Well first you got to have a Google account, log in your account on Google and go to Google Experimaental, just click on the "Join Experiment" button and start searching on Google.com.