Blogger and BlogSpot are being rubbish. I’m finding that requests aren’t being returned for a large number of users (which changes everytime) XML files. For the time being all Blogspot hosted blogs have been disabled from the site. Hopefully they’ll fix their end soon and we’ll get you all back on.
19:00 update I’ve changed the cache period from 25 minutes to 2 hours, so new posts may take time to appear. However this does seem to allow BlogSpot blogs to appear.