I found this paragraph "You still do not yet have the ability to connect your Android device to your PC or Mac and transfer titles via Adobe Digital Editions (needed for books such as those from your local library), but I am hoping this too comes in a future update that would really make me a happy ebook reader." on the site Boris links to above. So, there does not seem to be away to read those DRM file from other sites. Any unprotected, DRM free, epub shoud work. But you will need to copy it to the Nook folder, sub folder My Documents. It does not see PDF files.
Apparently the app will also sync to your Barnes and Noble reader on your computer, and pick up the last place read on the Android device.