This post written back in Feb 2008 remained unpublished till now. Here it goes...
My idea of a perfect job: Lay back and relax in chair in an air conditioned room, and keep getting your salary at the end of the month. Yes, get paid for doing nothing :) Too bad it does not happen in real life :(
Why does one want a challenging job? I don't know. If job is a challenge then it would bring a lot of tensions. You don't know how to do it but you are expected to finish it on time. How is that fun? That is a hopeless situation! I would want a job that requires you to do very little. And you get enough spare time to do challenging tasks that *you* really want to do, and not so called challenging tasks specified by your boss. Like participating in a coding contest. Like spending a week in a Topcoder marathon match. Or making a software that you really want to make. Things that you like to do will become boring when it is forced (by your boss) .
Or in other words, take a job where you do what you like and it won't feel like work.