I periodically weed out my main storage and Library, then add in the books I'm thinking of reading soon (from the Calibre library on my LAN or through my PC, but would be the same from an SD card). It's not as neat as being able to read right from the SD card, but it works!
Actually, I wouldn't want to read from the SD card, because I like the extra features available only when you add a book to the eDGe Library. And deleting is easy enough using the multi-select tool.
I see you got an answer to your "factory default" question over on the enTourage forum.
(
http://www.entourageedge.com/forums/...actory-default for anyone who's curious.)