[Alisa]

You can license up to six devices per book. The license is tied to the device (PID) not the account. So while you can download those books to your new device, you cannot reclaim the license you put on the device you sold. Remeber that each new device you put it on takes a license even if you delete the book off, so you may not want to put every book you own on every device unless you know you want to read it there. You may find yourself out of licenses if you upgrade or put them on your iPhone, etc.

As for leaving the books on the device you sell, I see no problem with that since you're not subverting the licensing structure that Amazon has provided.

Edit: Just saw Amazon's reply above. Missed that before. So I suppose it's a violation of ToS. Personally, I don't feel ethically obliged to delete them unless Amazon is going to give me a way to free up that license again.