Well here's something interesting...Tonight I open one of my FW epub's from B&N with winrar only discovered it was epub made with Calibre!
So I went back to original one with DRM still on it and sure enough it's Calibre version converted with calibre (0.6.16) from the opf.
So I opened up another one calibre (0.5.1) and calibre (0.5.14) well you get the picture....I had no clue B&N was using Calibre.
These are all straight from the nook site not added to Calibre. Open one up and take a look for yourself. You don't need to remove the drm to read opf in notepad.