Interesting topic for me in particular as I have just turned down a job promotion. Here were my reasons:
1) Money, I think the "more money" reason is a myth. Normally a promotion means more hours at work. If you break the wage down to an hourly rate. I am way better off (financially) in my current position, doing 38 hours a week as opposed to most management positions of 45, 50+ hours a week. (of course this all depends on the actually salary increase)
2) Family time, For me, this is higher up the priority order then money. I have a young family and absolutely want to be part of my children's life (whether they like it or not...hehe)
3). Enjoyment of work. I enjoy what I do, as Mark T states above, I much rather enjoy my day on a modest income, rather then hate my day for a larger income. For me, money is not the answer to happiness. I have been happy to work on large projects requiring up to 70 hours a week. The money was great, but I could only do it for short amounts of time.
Of course ultimately I understand that my long term prospect within the company maybe limited now (pissing management off), but that was a cost I was willing to pay.