How might they do it?

I was taking a look through CampFire ([url]http://www.campfirenow.com)[/url]. (If you don't know if it, just use an ajax "shoutfox" for reference I guess)

The system polls the server every 3 seconds for new messages/events/etc.

Unless I'm totally out of it, my thoughts are that each poll results in queries:
- Check for latest messages
- Check for members in room

That would mean 2 queries for each of the above every 3 seconds. Surely that isn't the way it's done though, as I would think that would create massively unnecessary serverload.

Any ideas how to more efficiently accomplish such a task?