You mean like http://dabbleboard.com ?
One thing I've often wished for was a standard syntax for specifying syntax highlighting modes. Right now basically every text editor has a different way of doing it, so you have to write dozens of modes when you create a new language or editor.
Thinking about it (going back slightly) there are not many situations where I see anyone actually coding with others in REAL time. Perhaps on hackathons (actually it would be ace for them) or suchlike - but for real work I doubt it would work. So the big selling point is gone: and there is nothing else to support it as a useful app (when Google docs has 100x the features).
That said I hope that will change in the future because it is rather nifty :D
(Yes, we could do that on public sites, but we're not going to, and neither are many of our customers).
Yes they have the handiness of true realtime updates (and I am not denying that isn't a huge feature) but that's hardly a unique feature (or wont be for long).
But then the rest of the UI / feature set is far too bland :( at least get some code highlighting and stuff in there.
Also in our short test earlier it didnt handle mass deletions & editing very well (if I deleted a block of text as someone was adding to it merry hell broke loose :P).
IMO a nice demo of a cool idea but badly executed enough to be no real use. Make me a real time white board and THEN I might take notice :D