I was convinced I wanted a flat bar bike, but a road bike fell into my lap a week ago and I'm finding that with drop bars I don't have the hand numbness that I was getting on several different mountain/city/comfort bikes with flat bars. It wasn't a huge problem if I moved my hands around, kept the weight off the palms, used the bar ends, wore gloves, etc, but drop bars have completely eliminated the problem. I still prefer the flat bar position, but i'm going to experiment with the stem height/extension and bar angle and stick with the drop bars.
obviously, most people can use a flat bar without their hands going numb. still, to me it speaks to an inherently more hand-nerve friendly set-up.