Originally Posted by TWiTCommander
making a mobi file from an epub is dead-easy if the epub file is properly formatted.
step 1: download kindlegen from amazon and unzip the file
step 2: open terminal.app from applications/utilities directory
step 3: drag the kindlegen executable (black rectangle icon) into the terminal.app window.
step 4: drag the epub file into the terminal.app window.
step 5: hit the enter/return key
you should get a mobi file in the same directory and with the same name as the epub file.
as mentioned above, using calibre is another option. however, i find calibre to be extremely slow on certain epub files, and competitive with kindlegen on others.
also, being a unix geek, i have a sweet spot for command line tools.
It's a lot easier to use Calibre to convert ePub to Mobipocket. One simple command from the command line and you are done in no time.
ebook-convert eBook.epub .mobi
Wait a few min at most and done.