Steamworks Info for Mod teams
Right now, Steamworks is a platform framework that's built for scale. It is appropriate for use in broad release commercial games, but we don't think it and our support infrastructure is ready for Mods or games likely to have a very small install base or just starting out with growing their user base. It's a bit of a judgment call on our part that we have to make but past history can give you some examples of Mods and games that have reached an audience size that we think can best leverage the Steamworks features (e.g. Day of Defeat, Counter-Strike, Garry's Mod).
Most of the tools and functionality included in Steamworks is intended to support games by including ancillary functions like cheat detection and DRM. Obviously, those things won't help you build a great game in the first place -- Steamworks is not intended as a game creation platform. If you're a Mod team, be sure to check out the Valve Developer Community. This site includes information on how to get the Source SDK, and is full of valuable information contributed by Valve and by teams using the Source Engine.
Steamworks, it should be noted, is not part of the Steam publishing/distribution arrangement. Steamworks is a free toolkit for game developers; distribution on Steam is handled through a separate deal with Valve.