Another program’s out there; this one written in python. The source is available from pastebin and I’m sure the usual IRC-type places as well. It’s unlikely that even 1% of Kindle owners know what I’m talking about.
Interestingly, Mobi’d previously given funny messages if you tried to use pdbshred, an older security-stripper for Mobi and Ereader files, on their DRM, so probably they or Amazon’ll refine the encryption/security algorithms to protected Mobi files, as well as the Kindle variant. But I wouldn’t expect another Dmitry here.
Class 4 of the anti-circumvention exceptions to the DMCA is still in effect, allowing circumvention should an ebook not be accessible for screen readers (the way all Kindle books are), and while Amazon is no doubt contractually required to offer solid DRM to at least some of their publishing partners, given the audience of Kindle, they’re way, way too smart to care. Besides, even the most optimistic bettor would take the over on just how many years it’ll take for the average Kindle user to discover the free Mobipocket library.
Related, somebody should do a thesis or something on just what percentage of Bookshare titles were originally commercial ebooks. Probably not too many, the Bookshare folks pride themselves on getting new releases into their lawful system of free titles for the visually impaired as quickly as possible, but it’d be an interesting study nonetheless.