To the devs: have you thought about using BOSH and ejabberd? That way you wouldn't have to poll for updates.
I built a little toy app that used BOSH and ejabberd to do chats - upside is you get all the extensibility of XMPP and the downside is that you have to deal with all the extensibility of XMPP. :)
Talker is more extensible, we're focusing on API and plugins http://talker.tenderapp.com/faqs/api, has inline feed notification for eg.: github commits, twitter search results, tickets updates in the chat room. And a lot more to come.