"Librarian" carries baggage, so I'm not going to try to change someone's perception in 30 seconds. They know we are somehow tied to books & library buildings. We are smart people who know how to answer tough questions. When I talk about what I do, I try to talk at the task level. Let them use whatever big picture they have already developed.
My elevator pitch goes something like, "I meet with people a lot; I consult on under-the-hood projects like digitizing books and building websites. I also teach and lecture on a variety of topics about digital projects. My main responsibility is improving our methods for storing digital files; it gets tricky when you get into the terabytes."
Then the conversation generally gets around to iTunes and software for managing pictures; of which I really have no expertise, but I toss out some fancy terms sometimes and offer general guidelines that you could just as easily find on Lifehacker.
Anyway--I really think focusing on your tasks will give a clearer picture than trying to sum it all up in one sentence about information and knowledge and access.