I'll also add that Amazon has two different protection schemes -- one on which unswindle works with, one which it won't. The other protection scheme that unswindle doesn't work with is called Topaz, which is a very hard-to-extract format. However, here's the site of a developer who has found a way around it it.
http://darkreverser.wordpress.com/2008/ ... /#commentsToward the bottom of the posts, you'll see links to download the latest versions of the scripts to un-Topaz the files, but as with unswindle,
you need to actually own the book on your Kindle or iPhone.
The reason I would want unprotect a book is not to share it (as I like that fact that authors get paid for their work!), but mostly because I either want to put it into TextAloud OR because I prefer much prefer the Stanza reader to the native Kindle app on my iPhone for actual reading.