If you don't mind piggy banking off of Google Reader, I've seen many apps that successfully use that as the aggregator. To have your application handle multiple feeds would be very resource/network intensive, in my opinion. A good example of an excellent Reader based app is Reeder.
If you still want to create your own custom aggregator solution, it still might be useful to work off of Google Reader to start (for development purposes) to at least understand how you'll handle multiple feeds rolling in. Also, I'd look into more server-side based solutions for providing that information as I still keep my opinion that handling that in the app itself would be excessive.