Android as HTML5 kiosk/appliance What's involved in transforming a rooted Android device (in my case, a Nook Touch) into a real HTML5 kiosk?

Meaning: The user never sees any part of the Android OS GUI elements; the screen is always just a full-screen browser window located at an HTML5 app.  When the device has to go to sleep, it doesn't change what's displayed on the screen, and when it's woken up the user is right back in the HTML5 app.
You can do that with the Nook, first thing is to get access to the Nook SDK, (not just android here):

https://nookdeveloper.barnesandnoble.com/

Next, you'll want to disable the home button, Stack Overflow has a good thread on this:
https://stackoverflow.com/questions/2162182/android-is-it-possible-to-disable-the-click-of-home-button

Lastly when setting up your Nook-esk Kiosk be sure to set it up in a way to keep it plugged in.  Kiosks should always be powered, and a full battery drain will reboot the whole OS.