web socket isn't that hard. I use it in my project. be sure what client(browsers) you are going to support, it won't work for Ie7&6 (or older chrome & ff)

1) socket.io 2) faye.jcoglan.com 3) eventmachine 4) xmpp

to use 1&2 is faster & easier, however, for example faye doesn't support event handler currently(but soon in v0.7 )

And faye also kind of hard to extend.

In my opinion, use redis(support pub/sub) & eventmachine (or something like it). to build ur backend.

use websocket-js for client.

:)