I've been pessimistic about B&N for awhile, though I didn't expect low sales like this. If the Nook stumbles, though, B&N is royally screwed.
We'll see how bad the damage really is when they file their quarterly report in February.
It's worth noting that Amazon has also had issues this year, and of course, being Amazon, they haven't explained why their margins tanked in Q3. We'll see if they got it together in Q4.