Someone needs to come up with an algebraic formula that includes the number of posts in a weblog’s RSS feed, the number of days in a row that all of the old posts in it show up as new, and the amount of mental effort it takes to unsubscribe from the feed to calculate how long a feed can stay broken before users unsubscribe en masse. I wonder if other people are like me — I generally unsubscibe without letting the person know that there was even a problem.
This is also a good reason to subscribe to your own feeds. I sometimes even consider subscribing to my feeds with more than one tool just to be absolutely sure everything is going OK. These days I think that feed usability is even more important than the usability of the actual Web page where your weblog is published.