I've had a fully functional forum for my RPG Icar now for 3 months. During this time, the forum has proved invaluable to my design as I can add notes and ideas on there and immediately get feedback from regular players as well as irregular players.

If you have a game and a website to go with it, I would thoroughly recommend a forum. Make sure you keep posting to it, though, otherwise people will assume the game has died off!

A short note, but I hope it helps someone!

(Like the Forge, I use phpBB)