Before I say anything, let me say I am a novice deer hunter at best (2 seasons). However, I am very serious about it, and even more serious about taking deer humanely. All of my hunting is done with a shotgun or muzzleloader using high velocity sabots. While this ammunition is excellent at achieving great groups, they are notorious for not expanding. After much research, I found a great article on the shoulder shot. Because of the heavy weight of sabots (i shoot 250 grains), they carry plenty of kinetic energy to punch through the shoulder blade. Unlike a rib shot, the shoulder allows the sabot to achieve quality expansion, thus increasing knockdown power.
One other point wanted to bring up/ask about. Some of the posts have talked about how the shoulder shot is riskier due to an accuracy standpoint (smaller margin for error). After looking at a cross section of deer, it seems that the high shoulder offers a great deal of forgiveness, granted you are using a heavy bullet with enough KE that is. For example, with the normal boilerroom shot, a few inches too far back and you have a gut shot. Shoot too low and you might get one lung if you are lucky. Either way, not a fun tracking job.
On the other hand, a shoulder shot that is too far back may just end up in the boiler room (in the lungs at least). You have to miss pretty bad to hit the gut with a high shoulder! A low shot with the high shoulder still puts you in the heart/double lung region. A high shot, you get the spine or nothing at all. The worst case scenario is the miss too far forward. With the high shoulder, a miss to the front of the animal still puts you in some neck vital areas (although i do not like head and neck shots).
Please let me know what you think, and again i'm not preaching, just trying to find the best possible way to take deer quickly and humanely.