See this link:
"It appears Barnes and Noble has introduced a new hardware revision or another change which is causing units to become bricks after running the official Barnes and Noble 1.0.0 firmware image. These units can be identified by the 10031 serial #.
A label on the bottom of the nook box will indicate what version your nook is.
If the serial # begins with 10031, the unit MAY OR MAY NOT be rootable. If the serial # is greater than 10031, it almost certainly NOT rootable.
If the device comes preloaded with firmware version 1.4.0 or earlier, it is likely rootable, regardless of serial number. If it comes preloaded with 1.4.1 or greater, it is almost certainly NOT rootable."
Edit: People say to disregard this info as it's badly dated.