This is a fundamental problem (likely intentional) with the nook's firmware. The book description only shows up for the B&N library books (bought directly from the nook and downloaded over the air into "My B&N library").
The "My documents" library does NOT have the ability to read most of the metadata that you and I
worked so hard to put into our books. Blame B&N for crippling My docs since day 1 and only grudgingly adding a few features (like search and author sort) after their customers raised hell on the B&N forum for a year. Even books bought from B&N and sideloaded into My Documents will not show the description. It's a transparent tactic to nudge people into buying directly on the nook.
If you really want it, I think the only solution is soft-rooting and using Trook or something like that. (I have not done that so please wait for advice from someone else before doing anything!)
Edit: from what RAH wrote, I have a faint hope that perhaps I'm wrong. So, if anyone really has seen a book description show up in "item details"
for any book (irrespective of source, history or Calibre/non-Calibre) in "My Documents", I implore you to post here
