This is cool. I have a Facebook profile, so I signed up to be a fan of Shaun's. (I am already a fan of David Tennant too.)
For those who are confused, Facebook and Myspace are called "social networking" sites. You can make a profile that has information about you, like your favorite tv shows and movies, and what your hobbies are. You can become "friends" with people on Myspace and Facebook (just like we have "buddies" on the Shaun the Sheep forums). Then, when you update your profile, or post messages about what you are doing, the website notifies your friends.
Here is a short video that explains all about how these websites work: http://www.commoncraft.com/video-social-networking