The global chat feature.
Steam has a similar feature that I suggest we start using. There is a feature called Steam Groups where users can create, you guessed it, groups relating to the games they play.
The largest group right now appears to be this one:
http://steamcommunity.com/groups/IL2COD
Steam Groups have their own chat rooms too, and the nice thing about the chat rooms is that you can simply put a link into the chat like this: steam://connect/1.1.1.1:27015
With your server's IP and anyone clicking the link will have their game start automatically which IMHO would be excellent for starting coops, etc.
Hope this helps someone