FeedBurner enhances your current RSS or Atom feeds in a variety of ways that YOU control, while simultaneously providing personalized usage and trend statistics that describe how your feed is being used.
A disclaimer -- I'm advising the FeedBurner team. That out of the way, here's a list of the current set of services that are currently offered up in their pre-alpha release: item level stats, link clickthrough stats, feed summary creation, auto Amazon link generation, browser-friendly feed rendering, content-type transformation and feed generation optimized for mobile devices. And they have big features on the horizon: authentication services, feedsplicing capabilities, namespace extension capabilities for richer content and general "future proofing" of feeds.
The upshot? Information publishers get to focus on content production, have their CMS pump out one single feed, and then let FeedBurner transform that feed eight ways from Sunday, extend it with new functionality, version it down for dumber devices, and while they're at it track feed usage along the way. Looked for newly burned sippey.* feeds coming to an aggregator near you soon...