I recently bought a kindle 4nt because there was a special amazon offer. Now I jailbreaked it and installed CoolReader as well as Liberator on it and I'm pretty happy. There is one thing that still bothers me: Here in the forums I read about amazons policy of collecting data while using the kindle, but I'm not sure if the method to stop them from it is appropriate anymore.
I own a Kindle 4 NT (black edition, 2012) with 4.1.0 jailbreaked.
I would be glad if the others would share experiences with that device with me.