When my friend mentioned something about farmville an antifarmville twitter started following her, when I mentioned something about Twilight a Twilight Fanclub started following me and it happened about a minute after I posted the tweet. I was just wondering if it was possible for people to automatically follow you based on what you say in your tweets?

Yes absolutely there are many software scripts out there, one of them is called Hummingbird where you enter keywords and then it starts following people automatically. However this can lead that many people dont like you to follow them and then block you, and as results your account could be banned.