[itronitron]

I've only experienced one whiteboard interview in six onsites within the past three years, so their popularity may be waning.

Also, there seem to be several different types of whiteboard interview, a) the algorithmic solution, b) the conversation starter, and c) the problem analysis. I mention this so that you don't focus solely on the algorithmic type, the other two really are there to help interviewers know how you approach problems.