I've been using a messageboard in connection with my games for a few years now.
1) We open a thread going for each adventure. I post quick session recaps there. The players post in-character in response. Folks don't always post, but when they do, it's a nice way to keep things going between sessions. It's particularly good for conversations with NPC's and for exploring non-lethal environments.
2) We keep an out-of-character thread going. This is the place for the player's to plan their next move, to distribute treasure, etc.
3) Google Docs are your friend. We have a google docs spreadsheet open to the whole party. One sheet has everybody's skill ranks on it. One sheet for everybody's powers. One sheet for everybody's equipment. One sheet for treasure that hasn't been distributed. Make the players keep it updated. Then start a thread and link to the spreadsheet in it. As the DM, it makes planning and running the game a lot easier for me.
4) I also use the google docs version of powerpoint to share maps and pictures. Again, open a thread and link to the presentation.
5) Goof off, swap stories, link to jokes, etc. etc. Pretty much what you would do with any other board.
