Mine as well and I also serve up my own little icon to let me know that I've thwarted them one more time.

Can you post a list of the other domains facebook uses?

I use this, not sure if that's all.

    # Block Facebook
    0.0.0.0 www.facebook.com
    0.0.0.0 facebook.com
    0.0.0.0 static.ak.fbcdn.net
    0.0.0.0 www.static.ak.fbcdn.net
    0.0.0.0 login.facebook.com
    0.0.0.0 www.login.facebook.com
    0.0.0.0 fbcdn.net
    0.0.0.0 www.fbcdn.net
    0.0.0.0 fbcdn.com
    0.0.0.0 www.fbcdn.com
    0.0.0.0 static.ak.connect.facebook.com
    0.0.0.0 www.static.ak.connect.facebook.com