The latest firmware update from Barnes and Noble for the Nook Tablet (version 1.4.1) disables the ability to sideload apps. This is an automatic update. Version 1.4.0 allowed an app to be pushed onto the device which enables Android Debug Bridge and thereby allowing true development of android apps as well as root access.
Luckily, restoring firmware will bring ADB and root access back. The process is quite simple. Download acclaim_update.zip from the discussion thread to your sdcard and start the tablet back up. Once you get the device rooted, disable the service responsible for automatic updates.
Thanks to Adam Outler for the tip!___________________