Asking someone to implement a solution to a problem which they have never seen before in thirty minutes  does not allow me to assess someones acumen as a software developer.

If all coding was done against the clock then this approach would be fine.  Writing code is not the same as working on a car production line.

****Actually writing robust code, which fulfils a requirement works by thinking about a solution to a problem, then configuring, writing, compiling, debugging, testing, and supporting the solution.

This process often “happens” under the pressure of a shipping deadline - but there is not a physical timer.

37signals - excellent Getting Real book has (which makes a lot of sense):

**You Can’t Fake Enthusiasm** Go for happy and average over frustrated and great Enthusiasm. It’s one attribute you just can’t fake. When it comes time to hire, don’t think you need a guru or a tech-celebrity. Often, they’re just primadonnas anyway. A happy yet average employee is better than a disgruntled expert. Find someone who’s enthusiastic. Someone you can trust to get things done when left alone. Someone who’s suffered at a bigger, slower company and longs for a new environment. Someone who’s excited to build what you’re building. Someone who hates the same things you hate. Someone who’s thrilled to climb aboard your train.

Food for thought.