Tags, Notes, and "I Like It" : Now in SharePoint 2010, a user can add tags and notes with any page which can be either public or private. A user can also mark a page if he/she liked that page. SharePoint 2010 adds two icons "I Like It" and "Tags & Notes" in all the pages to provide this functionality.
Ratings : SharePoint 2010 allows users to rate items within SharePoint site, such as ratings various items within Document libraries, custom lists, blog posts, discussions threads, etc.
Tag Cloud : SharePoint 2010 includes an out-of-the-box tag cloud which can be added to any page within the SharePoint site.
Newsfeed : Newsfeed is another features included in the SharePoint 2010. You can set the types of updates you want to get in your newsfeed. You can set this using the out-of-the-box settings section available within the user profile page.