I think puzzles are common at the interviews because hiring based on abilities is a bit looked upon (see for example this advice attributed to John Ousterhout:

I think puzzles are common at the interviews because hiring based on abilities is a bit looked upon (see for example this advice attributed to John Ousterhout: http://www.quora.com/What-are-the-most-profound-life-lessons-from-Stanford-Professor-John-Ousterhout/answer/Eric-Conner http://www.quora.com/What-are-the-most-profound-life-lessons...). Thinking goes that if you are going to build next google you obviously need to hire the smartest people and their abilities are irrelevant - they will figure it along the way. There is some truth in it but in practice even the smartest beginning programmer needs extensive coaching in minutiae of the craft and ramp-up projects of the right caliber (that is challenging but allowing sloppy execution and having essentially no deadline). And this coaching is going to take a big chunk of your senior engineers' time. So there is a big trade-off to consider. I suspect the main value of puzzles at the interview is to determine cultural fit - a guy who just codes will be uncomfortable among the types who enjoy puzzles (discuss them at lunch etc.).