If they're unrelated enough to not BE the actual book or movie, they're okay. There's a difference between basing an event on a book and sending the party off to cast a magical ring into Mount Boom and thereby defeat the evil dark Lord Moron.
It all depends on how it is done. The Lord of the rings plot was very well done. We were in the world and following the same plot line (for the most part) but it was up to us to decide what to do and to make it happen. LotR was so epic that it was actually exciting to be in that world.Otherwise I think ideads based loosely off books or movies are fine.