Granted the PDF converter seems to have some trouble with graphics PDF's, but for books the converter works very well.
Plenty of free e-books in Mobipocket format show up fine on Kindle.
The hack allow ENCRYPTED Mobi files to be read on the Kindle. So you can buy a DRM-protected mobi book and read it on Kindle.
Hack let you convert encrypted Mobipocket files that were intended for another reader so that that work on Kindle.