I've looked a bit at what it uses: shapes drawn are vectors, the app uses Raphael (http://raphaeljs.com/) for drawing, and Pusher (http://pusher.com/) for whiteboard syncing.
Regarding the Pusher web site, am I the only one who cannot resist the temptation of loading up Firebug to verify whether the counter is for real or "interpolated"?
Unfortunately it's not really viable to sent a counter msg for every msg which goes through the system ;) Our stats and logging has to be somewhat delayed.
I've looked a bit at what it uses: shapes drawn are vectors, the app uses Raphael (http://raphaeljs.com/) for drawing, and Pusher (http://pusher.com/) for whiteboard syncing.