There are four things that you can follow: People, Documents, Sites, and #Tags.
The vision for this release was that when you follow any of these four items, three things would happen:
- You'd have a rich, aggregated view where you could easily access the set of followed things and see additional information about those things.
- You'd promote serendipitous discovery of new people and content through the posting of a "User is now following Item" post to all of your followers (if your privacy is set accordingly).
- You'd see future updates about what you followed in the Following view of your Newsfeed.
Read more from source: http://sharepoint.microsoft.com/blog/Pages/BlogPost.aspx?pID=1060