The MobiPocket format is very close to being completely cracked. Aenea's
Secure Mobipocket Decoder currently relies on MobiPocket code and produces a HTML variant of the book, but igorsk's
demobi is written in python and just strips the DRM. The latter did not work on the one e-book I tried, but it did detect good PID's from unauthorized ones. For archiving, DRM stripping is all that is really needed.
If publishers were rational, they would stop distributing e-books with cracked DRM, although I suppose they can argue that DMCA still protects even inadequate DRM. It does not seem to have harmed LIT to be wide open (in fact it has probably increased sales), so perhaps cracking MobiPocket won't effect that format either. It is obviously a plus for readers, providing publishers continue to release new titles in the format.