I was able to grab the address http://geeks.campfirenow.com/ and I'll test it with a couple of friends.
As usual you can expect the clean look and interface that 37Signals have accustom us to. Only the minimum features are there, but for now, it seems very responsive.
Given the recent example of Zooomr regarding authentication (only the good parts, of course), I would like to see 37Signals start some kind of distributed authentication system, even its only on their sites. Right now, I have an paid Backpack account, a free Basecamp account and now a Campfire account. Time to unify all of them?
Anyway, the service looks good, but I'll reserve final judgement for tomorrow morning when a bunch of us discuss where to have lunch in a room in campfire.
One final question: why call something campfire and then use a lobby and rooms as your language? "there I was in a room at campfire" or "everybody around the campfire inside a room" does not sound good. I guess OfficeBuildingNow.com is not as sexy, but CubeFarmNow.com would be nice :).
Update: David Hansson commented on the single login across all 37Signals apps. His suggestion is that you look closely at the screen-cast posted in a previous Campfire article. The video crashed on my powerbook after a couple of seconds, I'll try to see it on another Mac, might be a problem on my side.