Apparently, if you stick a "www" prefix on the front of the URL for a BlogSpot blog, the URL may not work. So if you have BlogSpot blogs on your bookmarks or blogrolls, make sure to check that the "www" prefix isn't there.
(Kevin Drum pointed this out the other day, and I immediately thought, "A-ha! I wonder if that is why I haven't been able to load Highered Intelligence lately. Sure enough....)