We built a backend similar to this for our NewsRoom mobile client. (Android and Pre) Actually used some genetic algorithms to do the training for our content extraction, one of the more fun projects I've done.

Word of warning, if it takes off, you basically start turning into someone who is both caching and harvesting the web every 15 minutes. There is an incredibly long tail on RSS feeds and it starts killing you to keep them all up to date. Storing and serving it is no big deal, but harvesting actually turns into real money when you figure out total bandwidth used. (we harvest about ~30,000 feeds every 15 minutes)