Aaron Curtis from Indiana University came to BYU-Hawaii and did a presentation on his dissertation research. He is studying how much adding a whiteboard (Microsoft One Note) to a typical chatroom (Microsoft Meeting) can improve group understanding. Although his results are not complete, he says it does look promising.
I think the main advantage of the whiteboard was having an information store. With just an instant message, facts that have already been stated will scroll off the screen. With the whiteboard, the facts stay where they are. The whiteboard makes perfect sense when all of the information fits on the screen. It would be interesting to see what happens when it doesn't, and if some of the standard information visualization techniques would be enough to make it advantageous.