Bug#636292: MD5Sum mismatch is due to multiple DNS queries!
Oh my god even my "rock solid" rocky-mountain server is crumbling today:
W: Failed to fetch http://rocky-mountain.csail.mit.edu/debian/dists/experimental/main/binary-i386/PackagesIndex MD5Sum mismatch
W: Failed to fetch http://rocky-mountain.csail.mit.edu/debian/dists/unstable/main/binary-i386/PackagesIndex MD5Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
My theories are up in the air. My reputation is ruined.