We all Know about Facebook Like Button. So now Google has introduced its own rival, the 
+1 (Pronounced as “Plus One”) Button. It does almost the same function as the like button, only difference is that our recommendations appear on our Google profile page.
To add +1 button to your site just add the following code:
<script src="http://apis.google.com/js/plusone.js" type="text/javascript"></script>
<!-- Place this tag where you want the +1 button to render -->
According to Google:
+1 is shorthand for “this is pretty cool” or “you should check this out.” Let visitors recommend your pages right in Google search results and help your site stand out.
Various big and small sites has put +1 button on their sites. Google Has partnered with various sites for their +1 button
You’ll also start to see +1 buttons on other Google properties such as Android Market, Blogger, Product Search and YouTube.
The +1 Button also has an API for customizing it according to your site. Click Here To view +1 Button API
[Via- Google Blog]
