The iLibrarian blog had a great post
on mastering the art of the elevator speech with links to videos, articles, and even elevator speech builders.
I find myself using this tactic more and more- usually in response to, 'So, what do you librarians do now that everything is on the internet?' I find that a short promotional spiel about the continued value of librarians tends to go over better than hitting these questioners with, say, Goldman's Cecil Medicine
(3000 pages ought to knock sense into anyone!).