I have hunted with a lot of different people who have different opinions on how high a hunter should set his deer stand.
The biggest part of setting your deerstand is to set it to where you are comfortable. If you are not comfortable because your deerstand is way too high in the tree, most likely you are not going to be making comfortable shots.
My opinion though, I think the higher up you can get the better chance you have of not spooking a deer. I like to set my stands anywhere from 25 ft. to 32 ft. being this is the highest I can get without feeling a little uncomfortable being any higher. A lot of the guys I hunt with tend to keep there stands around 15ft. to 20ft. I have hunted a lot out of both heights and I seem to see and keep deer around me a lot longer when I am higher in the tree. There is a better chance that your natural smell is going to stay higher in the air and the deer are less likely to smell you out. The deer don't seem to pay attention to things that high in the tree. They just have a harder time seeing that high up.
So if you want to see more deer and have deer hang around your stand a lot longer, push that stand a little higher than most hunters do and you will see the difference yourself.