>> You really get to see how people think and will work on the job with questions like this.

Interviewing is hard and I applaud you for trying something newer and more realistic but I'd be cautious in thinking "spend 30 minutes designing a system and be prepared to defend your work with massive risk/reward hanging in the balance. Begin... NOW!!!!" is representative of how someone will work on the job. There are an awful lot of people who will solve the crux problems driving home after the interview or the next morning in the shower vs. on-demand.

Very true.

I certainly don’t say BEGIN NOW! It’s a conversation. I continually ask questions during the design and ask the candidate to speak about the decisions being made.

In all honesty this process can easily last more than 30 minutes.

This is not a hard problem for someone with the experience I want, and there are many different correct answers.

Agree. Its far more valuable to see how a candidate approaches problems than some memorized recital show. I don't expect perfection, but if their reasoning is sound that becomes clear fairly quickly. I usually also include some imperfect questions purposely to see how they handle that. While we wish client projects were nice and clean with orderly data and tight requirements, the truth is that is rarely the case. It's useful to see how the candidate responds to those types of things. I had one gentleman argue with me about one of those questions claiming you would never see primary and foreign keys between tables not perectly match in the real world. Well when you are matching data from entirely disparate systems, you typically do. Anyway I digress.