[nailer]

As a previous poster said 'can you do that? Have you done that?' is the first thing I look for.

I also look for people who know why rather than just how. I'm looking for someone who understands the platform (generally a flavor of Linux) rather than someone who is great at rote-learning commands (which a lot of lower-quality Unix people get by on).

Another poster mentioned APIs rather than languages, and I agree: on both sides of the table I've bonded with the other person over specific Python APIs and their benefits and drawbacks.

I use progressively harder questions like a lot of candidates but make sure that the interviewee understands this, so they don't feel as if we're wasting time on the simple stuff or above their heads on the really difficult final questions.

I also look for people who are still passionate about technology outside of work. This rare, but sorely needed, in corporate environments.