This replay tool simply loads up a big batch of actions and plays them from the client. Once the page is out the door, we never hear back from it.

Twiddla itself uses good old-fashioned polling, along with a crazy fast message dispatcher on the server.

I'm still not sold on Comet. It's cool in principle, but you essentially need to build your own webserver if you want to do it. Personally, I'd rather simply handle 2000 tiny requests per second than try to juggle 2000 simultaneous open connections. Naturally, there's a bit more lag with polling, but in Twiddla's case it's hard to notice.