More on the purpose of Reading Lists

I’d like FeedLounge and Gregarius to support Reading Lists.  The key is that feeds will drop in and out of a given reading list transparently.  I can understand some of the technical difficulties.  What if your aggregator only understands that a user is either subscribed to a feed or he is not.  What if a feed can only belong to one folder?  I don’t think that stuff matters.  Reading Lists are here to stay, so the backend needs to support them.  Dave explains, yet again, why they are important in this post.