Now try this: hide your Nook's USB charging cable. Let the Nook's battery completely drain so that the Nook won't turn on.
Plug in a generic USB cable and charge all you like- hours, days, whatever. Try to turn the Nook on.
OK. It's charging.
With the screen on full bright and the governor set to performance,I started up StabilityTest and let it run until the tablet turned itself off. When I tried to turn it on, it told me to charge the battery and turned itself back off.
Then, in the most likely scenario, I plugged it into the $5 Walgreens charger through my generic USB data cable for one hour. Turned it on, waited for it to boot, and went right into Tablet Status. The battery was at 23% and charging.
I didn't choose the $5 charger randomly for this test. I chose it because my Droid X is notoriously picky about chargers. Since it works with my X, I was confident it would work with my Nook.
I suspect folks are trying to use chargers that lack sufficient oomph to trigger the charge controller. My $5 charger's output is rated at 5V (verified - no load) @ 1A. I've also got a few that put out between 4.1 and almost 6V. I didn't try them in this test because they don't charge my X. I'd say the Nook is somewhat more forgiving in that respect.
After all is said and done, you can be confident that with a decent charger and cable you *can* charge the Nook. You just have to be patient because it will take longer than it will with the OEM charger and cable.
YMMV. Results not typical. Consult your physician. Yadda, yadda, yadda.
Now where did I hide that cable...