Thanks for the info on the screen flicker issues. I agree it's most definitely NOT normal.
The Nook Color I returned had this problem to a very slight degree, but it wasn't until after I got my replacement that I realized it shouldn't have been doing it at all (my reason for return was due to something unrelated to the screen).
I observed flickering with the device plugged in and detached from power. It was very easy for me to reproduce it - pretty much every screen was flickering, with the exception of a bright screen with light colors. Night mode and dark grays were the worst.
I went to a brick & mortar B&N (the first device was from the website), exchanged the NC and the new device had the exact same problem.
I didn't really have time to keep swapping devices until I found one without a defect, so I returned it for a full refund.
B&N should take particular note of this issue. It is obviously not isolated.
For now, I'm going to hold out to see if B&N acknowledges and addresses this matter.