Adding +1 buttons to your pages is a great way to help your content stand out in Google search. By giving your visitors more chances to +1 your pages, your search results and search ads could show up with +1 annotations more often, helping users see when your pages are most likely to be useful.
In the common case, a press of the button +1’s the URL of the page it’s on.
From the Google Blog -
If your site primarily caters to users outside of the US and Canada, you can install the +1 button code now; the +1 button is already supported in 44 languages. However, keep in mind that +1 annotations currently only appear for English search results on Google.com. We’re working on releasing +1 to searchers worldwide in the future.
If you have users who love your content (and we bet you do), encourage them to spread the word! Add the +1 button to help your site stand out with a personal recommendation right at the moment of decision, on Google search.