In another thread I gave myself the idea to build a multiuser whiteboard. I decided to do it, implementing my jChat as a base and build off that. I think it worked out quite well.
http://jsites.no-ip.com/jBoard/index.html
What do you think?
Edit
Just as an afterthought, I have noticed that the server (my personal one that I run from home) cannot handle a HUGE load, and sometimes will shutdown, but thats if you like, sit and scribble for extended periods of time.