The new player on the Web 2.0 scene? Ajax improved the UI, Comet seems more server-side oriented. Via a persistent HTTP connections it making the communication with the server “push-based” – the server, asynchroniously pushing data to the client side, based on some events. Better than Ajax for community-driven applications.

Bad according to some ppl, it can be just an Ajax pattern – HTTP Streaming . Still pretty long and informative discussion on Digg .