In my favorite cycling magazine, Road Bike Action Magazine, there is an interesting article about stem height. It talks about what it can mean for performance and the stigma of a high stem.
Evidently, there are some clubs/teams/groups out there that evaluate new riders based on their stem height. If they have spacers, they are viewed as inexperienced. I find this completely ridiculous. Yes, I do have spacers, but that isn't the point.
Those people who ride with no spacers and haven't had a professional fitting are only doing this to look like a pro. Most are not doing it because it is the best position for them. Also, stem height is only partially responsible for the final position. If a person has long legs and a shorter torso, then the rider may need spacers just to give them the correct "pro" position.
Anyway, the point of the article is that pros are able to obtain that position because they work to be flexible and to powerful core muscles and to be thin so their bellies (or lack there of) don't get in the way of their thighs. For us everyday Joe's, we are not as flexible and our core muscles aren't as strong, not to mention that most of us don't have sub 8% body fat.
So, if you see someone who has spacers, don't make any judgements. Also, if you don't have spacers and are having neck or back problems, or your thighs are hitting your belly, you might want to think about a professional fitting. Greg at Spin Doctor Cyclewerks does a great job with fittings.
Also, pick up the latest edition of Road Bike Action Magazine. I read it cover to cover and love it. Bob Roll is one of the regular columnists.