The widgets aren't served by WWW. Try something like to block everything:
# Block Facebook
127.0.0.1 www.facebook.com
127.0.0.1 facebook.com
127.0.0.1 login.facebook.com
127.0.0.1 www.login.facebook.com
127.0.0.1 fbcdn.net
127.0.0.1 www.fbcdn.net
127.0.0.1 fbcdn.com
127.0.0.1 www.fbcdn.com
127.0.0.1 static.ak.fbcdn.net
127.0.0.1 static.ak.connect.facebook.com
127.0.0.1 connect.facebook.net
127.0.0.1 connect.facebook.com
127.0.0.1 www.connect.facebook.net
127.0.0.1 apps.facebook.com
You can also block the widgets without the site (I log in from time to time but haven't seen a widget in a very long time). These days the like buttons are served from connect.facebook.net I believe.
