Yes I've seen it. In my case the book publisher was clearly at fault because the book cover image was only a partial cover, and it was not even the proper image at that. I used Sigil to look at the cover image and discovered the publisher's error. I downloaded the correct cover image, added to the Book via Sigil, and now it displays correctly.

However, I must state to make the correction I first had to strip the DRM, which I do for all my books. Also my book was purchased through the Sony Reader Store, not B&N.

In conclusion, the fault lies with sloppy publishing and not with the nookcolor or the B&N store.