I've had the server on my favorites list since Jeff tweeted about it the night it was created. I've been on it for a total of 5 minutes or so, and the entire time was spent waiting for more people to sign on to join me. Getting servers popular is an extremely difficult thing to do, since people will almost always choose mostly-full servers over empty servers.
In my mind, the best way we can promote the site is play on it. Advance-scheduled Game Ons will be useful for this, but only for a few hours out of the week. Is there any precedent for having pickup-type Game Ons? Say one of the admins of the steam group is interested in playing, an event starts immediately and notifications go out to the group members. If I were looking to play, I would be much more likely to get on the gaming.SE server if I knew that there would be people there when I get on.