About a year has passed since Facebook “Like” button started appearing all over the web. Now Google is rivaling it with the +1 button – the latest feature of Google’s Social Search. +1 was released about a month ago for a small percentage of U.S. search users, but a wide release is coming soon.

How it works. The +1 button will appear next to all Google search results. You can click on the button to recommend the site. Google will display the aggregate +1’s a website has received as part of the search listing, and also show +1 recommendations from your friends and contacts. You just need a Google profile to participate.

Social Search has already personalized the Google experience in that results can vary from person to person and include content created or shared by people in your social network (Twitter, Facebook, etc.). +1 will take it a step further by calling out sites recommended by people you know if they are part of your Google Network (Google Talk friends, Gmail contacts, anyone you are following in Google Reader and Google Buzz).

It’s still too early to tell how this will catch on, but here are a few important things marketers should know about +1:

• Although your personalized results may vary, it is not clear that +1 recommendations will impact rankings in general. That said, anything that increases click-through rate (CTR) seems like a prime candidate in this regard.
• The +1 button will also appear next to Google PPC ads. Advertisers will not be charged for clicks on the +1 button, but stats will be available so you know which ads are getting the most +1s.
• The Google +1 button will also be available to all sites, making it easy for your visitors to +1 your web pages.

To participate in the experiment and see the +1 button in action, go to http://www.google.com/experimental/index.html