Appearing as a small icon next to each search result and text ad, logged-in users can share their recommendations with contacts through their Gmail address book, Google Reader and Buzz contacts and, eventually, Twitter contacts. Google is characterising Plus One as a different function to Facebook's Like, saying that recommendations are only shared within the context of relevant searches, rather than spamming all contacts.
Social media is widely seen as the next generation of web services, but Plus One will also begin to influence the ranking of sites within search results listings. Users will be able to choose for recommended sites to be more visible in search results. Google is also planning to extend the service to news publishers so that they can integrate Plus One on story pages.
As with anything else, it'll take time to find out whether this catches on - but for sites with large communities of users, it might be a good idea to deploy this device and see how it goes. Get in touch to talk more......
Find out more at the Google Plus One Site