Perhaps this has already been noted, but you can now submit games to be added to Steam via the Steam Greenlight mechanism. If your submitted game obtains enough votes from users, Valve will add the game to their Steam service:
http://steamcommunity.com/workshop/about/?appid=765§ion=faq
This seems like an excellent way to promote Smokin' Guns and obtain more players.
PS. Valve accept mods, not just normal games. =)