Rule one: Make a backup of your factory fresh Nook ROM.
Linux/Mac: Become root
Boot nook with noogie.img and connect to your computer via USB.
New link here
use df -h to get your nook's /dev/sd? address.
typically something like: /dev/sdb
use diskutil list to get your nook's memory address.
typically something like: /dev/disk3
Once you know the address, unmount the Nook.
Linux: umount /dev/sdb* OS X: diskutil unmountdisk /dev/disk1
Linux: dd if=/dev/sdb of=my_backup.img bs=1M OS X: dd if=/dev/disk3 of=my_backup.img bs=1M
dd can wipe your computer's hard drive, so be careful! Make sure your're plugging the correct drives into the command above.
Restoring your N2E to factory-fresh is a simple reversal of the commands above:
(boot with the noogie sd card first!)
Linux: dd if=my_backup.img of=/dev/sdb bs=1M OS X: dd if=my_backup.img of=/dev/disk3 bs=1M
This wipes your N2E, restoring the specified image file.
Windows users, see the next post.