I jailbroke my KP3. The best thing that I'm able to mount my kindle storage on my laptop using SSHFS and use it to transfer e-books, modify ebook-metadata using my Linux machine, all wirelessly.
I was also able to cross-compile
https://github.com/Blub/netevent for my Kindle and use my Kindle to remotely control the mouse pointer on my Linux machine and my android phone! Not very useful to me but I sure learned lots of stuff along the way.