As a player, I like having a reference for things like setting information and house rules. And I am a somewhat extreme note-taker (it's funny what 23 years of school will do to you!), so I also like to put notes about what happened somewhere that the other players can read. (The notes can also be helpful for the GM.)
Obsidian Portal has pretty convenient tools for putting up session logs, adding comments, tags, etc. It also has forms pre-designed for many game systems. One of the games I play is up there (not RM), the RM game I play has a site on Google Sites which predates OP. That doesn't have the character forms or tagging, although it is pretty easy to add content.
I'm not sure if I'll set up something for the game I am running, it's really only useful if someone is going to put data in it. Depends what kind of players you have. I don't know that I want to take notes for the players, it's their job to keep track of the things they think they need to know... For the setting and house rules, I gave them a book in PDF format. It's already a bit excessive.
