So, many months later, I've settled on a solution that works very well: EtherPad.
They did a pretty substantial redesign and it has everything I need. It's browser based, free, instant, realtime, and it even holds revisions which can be played back in a time lapse view.
Brilliant!
2012 UPDATE: So, apparently Google bought, absorbed, and shut down Etherpad. Thanks Goog!