I've been using Shieldhaven's Wiki for a good while now, though I've let the campaign log slip out of date. Every once in a long while, one of my players actually remembers that there's a website. =)
Since my group is spread out over three cities, it proved easier for us to keep in contact and advance certain aspects of our campaigns by setting up a messageboard. Every week there are anywhere from 3 to 3 dozen entries -- clarifying details of the campaign setting, creating new NPCs, "sharing rumours", and the like.
The non-game stuff we do be e-mail and phone calles.
The tabletop game I run has an e-mail list. Another game I play in has a blog community. But those are just for inter-player communication for scheduling.
Now, one of the larps I play in has a world-wiki, character blogs, and several mailing lists for discussion - but the game is 60+players, and will run for at least three years, so keeping notes is kind of important.
Yes and, when playing, used regularly. I upload PDFs of house rules, campaign journals, etc. I also change the frontend for different campaigns. Right now, I'm customizing a CSS frontend for the planned Scarred Lands game and a separate one for our EZ20 one-offs.
I want to get a site up, but I haven't convinced myself to pony up the cash for the features I want. I'd like to have a messageboard, polls, a file download section and a wiki to use as an encyclopedia of the campaign. As is, I keep my house rules, session journal, and all my personal campaign docs in Google Docs, so I can at least publish the ones I want and send the links to my players.