I've seen something happen randomly, I addressed it in another post:
On occasion the touch screen sensors do not turn off when the Nook goes to sleep.
Whether this indicates that nothing has gone to sleep or just that the sensor has not gone to sleep is unclear.
Still, you can lose about 4% of a charge per hour overnight.
If you run into this, there is something that you can try:
adb pull /data/data/com.android.providers.settings/databases/settings.db settings.db
sqlite> update system set value=0 where name='stay_on_while_plugged_in';
adb push settings.db /data/data/com.android.providers.settings/databases/settings.db
3 is the normal value, telling the Nook to stay on always with USB or charger power.
Unfortunately, once a charger/USB is plugged in it gets its state all confused.
Even with this set to 0 the screen sensors stay active while plugged in.