I subscribe to some newsfeeds for pure entertainment value, and I don’t care if I miss an article, or dozens/hundreds. It would be GREAT if I could set an automatic “mark read after X days” on each subscription. That way these feeds don’t get stale or show up in my all items feed.
This would be a very useful feature for any feeds that contain time sensitive information, e.g. FX, commodity prices, share prices, discount offers, coupons, traffic or weather alerts etc. All these types of feeds contain information that expires or becomes irrelevant after a known period.