A quick test

With a shortage of much of interest to report (and given the stir the 'Monty Hall Paradox' created) - a short and very simple question;

Whay are man holes round?

I have throwwn this at people in interviews in the past and judged them horribly by their reaction to the question! If you don't get it within 30 seconds - chances are you won't - but if you're not busy, feel free let it bug you.

Answer in the next day or two.