Yeah, I stumbled on that just a couple of days ago after reading an article by someone flaming PollingDuplex and calling it a "toy". I'd spent a few days getting a chat variation going and was relieved to see Tomek's experiment showing that it could at least handle *hundreds* despite it's polling nature. Also, in most scenarios you'd need to store the callback reference on the server service so adding multiple servers for redundancy would be complicated, yes? Still, it's a welcome ability. There are apparently some other more scalable solutions, such as this: http://www.kaazing.com/  but I don't know anything about it firsthand.