They've been updating the B&N version of ereader continually, so hopefully sideloading ereader/fictionwise pdbs is somewhere on the horizon and they just haven't gotten to it yet.
Ironically, I can load up books from fictionwise, Reader, and Barnes&Noble onto my old Palm TX and read them all with the same eReader software.
One wonders what is going to happen with the epub mess. I was excited when the first B&N book I got loaded painlessly into my old ereader software. I was less excited when the second book was in epub format, without warning or any means of knowing prior to purchase and download.