Maybe it's been broken for a while, but I've noticed if one hits the "comment" links from the main feed, the aggregation of everything, a 404 error occurs as it can't find the post for the comment. It seems the blog name is missing from the comment; it's there in the "read more" links. I'll see if I can find and fix that. It's probably related to the blog breaking that happened during the upgrade the other day.