Three years ago a post was made about misbehaving sites:
https://getsatisfaction.com/newsblur/topics/notification_for_misbehaving_sites
As it is now, I am not being notified of misbehaving sites, when I am constantly viewing my feeds in “unread” mode.
Samuel, You mentioned that Newsblur would fix misbehaving sites, but sometimes an RSS feed is simply just shut down.
An idea to solve this, is that if a site misbehaves for e.g. 48 hours, it will show up in the unread view with the yellow exclamation mark. This way, users are properly notified about feeds that do not work anymore and they can actively try and solve it.