Anime By The Books and Iwa ni Hana had their feeds broken for a while. Their <rel=> links point to URLs that return 404. It's not a big deal only because both blogs are half-dead (I stopped visiting Iwa ni Hana when the Chinese bent started, but kept it in the bottom of the feedlist), and in fact it's probably not coincidential to that. But I saw active blogs doing that before. Don't let it happen to you.