I too have run the jailbreak on my Kindle PW and confirmed that it resulted in the "you are now jailbroken!" book being added, making it seem like it worked!
My question now is can I start doing the "update your Kindle" trick to get things like USB networking and SSH working? I don't mind experimenting and reporting results, but I'd only like to take the risk if there's a technical reason why it should work. Hopefully someone more familiar with this topic than I am can take an educated guess?