FWIW, an acquaintance of mine worked on one of the early RSS readers (Bloglines, I think). He mentioned that they had run some analytics on their users and found that the typical user would join, add a bunch of feeds, then slowly add more feeds over time until they had a ton of feeds and then would either delete a bunch of feeds or quit using the reader entirely.

I found that kind of funny. They were clearly deriving value from the reader, or they wouldn't've joined or kept adding feeds in the first place; but if they were feeling burdened or oppressed by their reader, why didn't they just stop adding feeds? Or if they had to keep finding new feeds, prune back the old feeds a bit. Why load up on feeds until you need to do a burst of spring cleaning or quit entirely?