1)Download and install Kindle for PC (Or Mac, if you have a Mac)
2)Download and install freeware Calibre (Open Source) (http://calibre-ebook.com/download)
3)Download and install DRM removal plug-ins for Calibre (if you use Kindle for PC app, you will just need to add the Kindle plug-in to Calibre)
4)Download your .AZW (Amazon's proprietary format) ebook onto Kindle For PC
5)Run Calibre
6)Find the folder with Kindle for PC ebooks (My documents/My Kindle Content)
7)Select DRM-protected AZW files and drag-n-drop them onto Calibre
8)Calibre will remove DRM protection from AZW ebook(s)
9)Convert your DRM-free MOBI ebooks to any other format (like ePub/fb2/LRF/Mobi/PDF/PDB/TXT/RTF/LIT) using Calibre if needed.
10)Enjoy reading the book in your new format. This is another way to say 'fuck you' to walled gardens like the Kindle.