[fishtoaster]

I used to think estimation questions were useful. I still think that estimation ability is something a programmer needs for exactly the reasons you state.

However, I used to ask one estimation question (How many hours have you spent coding over the course of your life) on all my interviews. Over time, I lost interest in it because almost everyone got it "right" (took an acceptable route and arrived at a reasonable estimate). The only people that got it wrong were ones I decided to reject for other reasons (this being a semi-technical but mostly ask-about-experience phone interview).

So, although I agree it's a useful skill, I don't think it's worth askin estimation questions from my personal experience.