WHAT IS GOOGLE +1
Google +1 was created as Google's response to the Facebook "Like" button and represents an attempt from Google to grab a piece of the social pie. As 90% of customers trust the opinion of people they know and 71% of customers are influenced by parents and friends in their purchasing, Google thought to improve its search experience by introducing the concept of social search.

+1.jpg BENEFITS FOR THE USERThe +1 button allows the user to recommend a search result, a website, a video or other online contents while allowing his Google contacts to see that he has "+1d" a page. It is a way for people to personalize their search, decide what is relevant online and share information with their online connections at a very low effort (the effort of one click) while providing them with a high value endorsement (the one of a person they know).
HOW DOES IT WORK FOR THE USER
In order to use Google +1, the user needs to own a google account and be logged in. When he searches for a topic, the + 1 button will appear:
  • Close to his search results
  • Close to google ads
  • On third party websites

The user can choose to recommend the search result on Google or the Google ad if he thinks they are worth it a check out. Alternatively, he can click on the link and visit the personal website, where he can also find a +1 button and recommend the web page.
After the user has clicked on the +1 button, Google allows his contacts from different google products to visualize the recommendation on search results and google ads everytime they search for the same topic. At the same time, the user will have the content he has recommended saved on his google profile and keep track of the websites he found relevant.

BENEFITS FOR THE WEBMASTERS
Google +1 is one of the many social signals to rank webpages, therefore it will help high quality websites to get a high positioning in Google search results. Independently from the page rank, Google +1 increases in fact people interest in recommended websites, because users trust more the opinion of people they know and esteem than the results of an algorithm. In this way, the click through rate of certain pages will increase, with the result that the quality score of those pages will improve significantly.
At the same time, the +1 button will bring more quality traffic to its clients, because it will spread a virtual word of mouth among people sharing the same interests.

HOW DOES IT WORK FOR THE WEBMASTERS
People with a Google account can add a "+1" button to their personal websites, typing the following url: http://www.google.com/webmasters/+1/button/. At that point a window similar to the one in the picture will appear, where they can personalize their +1 button.

google-plus1.jpgf4a2a_plus-1-metrics.png
By coping the underlined code on their webpage, they will have the +1 button available on their site and improve their page ranking. Through the number of +1 they will receive, they will have real time metrics available to evaluate the effectiveness of their campaigns or other online marketing intiatives and take corrective actions immediately (see picture).

BENEFITS FOR GOOGLE
Google will be probably the one who will get the main benefits from the introduction of the +1 button. One of the main advantages is that it will be able to get a more realistic, credible and real time feedback about what users want, which will be useful to define new algorithms. It's not unlikely in fact that the +1 button will be used in the future to determine the quality score of a website, independently from the CTR.
Moreover, from now on, Google will incentivize its users to log in their Google account in order to use the +1 button, with the result that it will be able to segment them more accurately, thus increasing the effectiveness of its online advertising system: Adwords.
SEE ALSO
Best practices of user experience on GooglePlus
How Google ranks the advertisers
How to design a SEO strategy
Why is SEO Important
Synergies between search, social media and mobile marketing
Why Facebook adds offfer hyper-targeting possibilities
Overview and key features of Google Analytics