Rich Salz covers the technical details, plusses, and minuses of RSS. Among a bunch of other issues, Salz highlights one that got swept under the rug in all of the political wrangling: HTML/XML embedded in RSS feeds. Salz points out that the Atom (nee NEcho) format at least cleanly handles this problem.
This is a fairly important issue for RSS as the final result can make it either much easier or harder for tools to deal with the format. However, as discussion within the NEcho community shows, there's not an obvious solution.