The best piece of technical interview advice I've ever gotten: It's much more impressive to NOT know something, ask about it, and then be able to understand it and apply it to your answer during the course of the interview, than it is to just already know it.

agreed, a few weeks ago I was interviewing and the interviewer schooled me on python generators and cooperative threading (pretty much all my knowledge is around erlang and message passing / explicit threading)

I got the job, and learned something along the way