I think the coolest part about the Nook Color that made it an excellent tinkering device was the fact that if a bootable image was present on the micro SD card,

I think the coolest part about the Nook Color that made it an excellent tinkering device was the fact that if a bootable image was present on the micro SD card, it would always load the image over whatever was on the system's eMMC. The Nook Color was therefore essentially un-brickable as recovery was always possible via SD.