the <cloud> element solves the problem of polling, it lets you subscribe to feed-updated notifications and read the feed only when it changes.
also, Atom has threading and RSS has some community efforts underway to make "replies" decentralized and aggregable (new word) http://xmlns.inreplyto.me/
also, Atom has threading and RSS has some community efforts underway to make "replies" decentralized and aggregable (new word) http://xmlns.inreplyto.me/