American Rifleman had an article by Finn Aagaard on hunting with .223 a couple of years ago. One of the biggest things is to get ammo loaded with bullets that are designed for heavier game, instead of varmints.
Finn was, however, shooting southern whitetails, which are generally smaller than the northern whitetails. I personally wouldn't do it on Northern whitetails, I just don't think it gives enough "safety" margin to make a clean kill.
As trjake notes, you have to be VERY careful in choosing your shots.
I'd rather use .25 or .30 caliber, and have the option of taking those less than optimal shots, such as a quartering shot.
If you go for head shots, and can make them, then .223 is just fine.