The Simple Sharing Extensions built by Ray Ozzie at MS is
a pretty decent description of nearly Web-native pub-sub message handling. Anyone doing event notifications will recognize most of the issues and algorithms - there are some very useful wrinkles when considering the context of RSS and feeds.
One thing that this doesn't improve on is the retrieval of data from a single URI - multiple consumers have to really keep up their polling. An alternative is to use something similar to Atom's next/prev linking (which I'm not sure is in the final Atom spec, but it's in the discussion history somewhere). In the case of MS's SSE, if each incremental feed was located at a unique URI, and that feed contained a link to the next set of changes (that the server chooses to hand out) then a lot more caching can take place and the server can choose it's own approach to throttling clients.