The nice people at Mobileread say that cracking .mobi is easy, but then they start babbling about installing a specific version of Python and how to find the right scripts now that the last spot was DMCA'd into oblivion, so I think maybe they mean "it's really easy once you've done it half a dozen times and set up a couple of friends' computers with the software too."

If I'd bought something and couldn't get it to work right, I'd feel no guilt over downloading a cracked version from somewhere else.