This link says that Facebook sharing works only with B&N books, not sideloaded books, but it is a year old. Possssibly things may have changed since then? (Probably not, I admit.)
http://bookclubs.barnesandnoble.com/...C/td-p/1283955
Just checked with my Kobo Glo - facebook sharing of sideloads works on that. Hopefully someone with a Nook will be along soon to test for you and give a definitive answer. (It's possible that a clearer thread title might speed that along.)