So:
You can turn off the kindle without it rebooting if you have jailbroken and run
in kterm (KUAL extension). I just tried it.

It displays the "Please wait a minute while your Kindle restarts" message, but doesn't turn back on like it normally does. Thanks dsmid for the info.

This can be bundled into a KUAL extension easily, if it hasn't been already.
Just curious what does the kindle execute when Menu ==> Settings ==> Menu ==> Restart is used? Or when the hardware button is pressed.