I've got it loading now, hopefully be able to report back a little later about the results

.
I can confirm that it doesn't open a epub B&N book downloaded directly from their page. Not sure about on that was pulled down with their reader software (those have a number on the end of the filename, where the ones you download directly from the page have my first 4 letters of my name on the end of the file).
Don't have anything I can load that is a drm'ed epub file for Mobireader yet, so can confirm that or not.