Its been my experience that trying to interview someone by playing the "Stump the Chump" game only gets you someone who might be very good at trouble-shooting, but may lack any strategic knowledge in the day to day essential work. Take your example and suppose you had a guy come in who could debug and resolve your VM installation - does this mean that the next time you are charged with a major project that requires design, vision, and intuition that this "McGyver" you just hired is going to be your person? I don't think thats any kind of overall indicator.

For me personally, I am most impressed by people who show me their work. I am even more impressed by someone who shows me their work and is excited about it. On the other hand, when a candidate comes to an interview with nothing to show, I worry and frankly, its a strike against them. I want to see someone "sell" me as to why they are the best candidate, and their work speaks volumes to that (or not). I don't need any installable - even screen prints, query listings, illustration of projects - these things impress me (most of the time) and the lack of them does just the opposite.

However, we have found our biggest success with SQL candidates (DBAs or just line workers) comes from 1/2 day interviews where the candidate meets various team members, each testing different areas of knowledge, and then we all get together and discuss whether or not we have a second interview candidate - or a person who will not make the cut. In these extended interviews we get to judge team-fit, as well as skill set and aptitude for being a positive contributor.

This has worked very well, avoids the "Stump the Chump" game and usually highlights not only SQL skills, but the crucial team-player skills we seek.