He may be giving Radio’s aggregator short shrift, but Jeremy has done a good job of breaking down several approaches to RSS aggregation and providing his own wishlist:
I’m on a quest to find the perfect RSS aggregator…. I’m thinking of a server-based process that can gather all the data and give it to me in one of several ways. Maybe I can just point my browser at it and catch up on the news—just like AmphetaDesk. That’s great for when I’m on-line and in a surfing mood. I’d like it to do RSS auto-discovery. I’d like the option of having updates sent to me via e-mail and possibly instant-messenger. Heck, I’d like to be able to subscribe via e-mail or IM as well…. Anyone know of such a beast? Sounds like it’d be a fun project to build.