I learned about this over on Baen's Bar, where someone with eReader for his PalmOS device complained about buying an e-book in good faith and expecting it to be in eReader format, but finding it in eReaderPub instead.
I went to B&N to investigate, and
wrote my findings up in TeleRead. There is no hint on B&N's e-book pages or in their FAQ that they've shifted away from plain-vanilla Fictionwise eReader, and a couple of hints that suggest to the uninformed that they haven't.
(The name "eReader" is triply confusing now. Not only is it used by the uninformed to refer to e-book readers in general, but now there's Fictionwise's eReader
and Barnes & Noble's eReader, which use different formats. Oy.)