Quartering towards me, at say 20 yards or less and if I didn't think the deer was going to offer me a better shot, I'd take it. I am confident that I am going to put the arrow where it needs to go and I am confident that my set up is going through the shoulder if impacted. For the record, I am producing 70 lb. of KE and using a Slick Trick broadhead
Straight on shots, I'll never personally take one. Like someone said, there's a lot of bone in there to get through. If you get through, the deer's dead because there's nothing but vitals behind there, but if you don't get through, you've got a bad situation on your hands. This being said, I know guys who routinely take straight on shots, I don't condone it, but it works, and the theory makes total sense. If you aim at the base of the neck, you're going to cut the wind pipe and even if you'd don't get through the chest, you're going to hit an artery.
This being said, it does pose a question in my mind. I have seen a bunch of videos in which straight on shots were taken with guys shooting 60-65 lb. bows and using Muzzy's, Rocky Mt's and the like. I've seen it done to whitetails, mulies and a few other animals. On every shot the arrow zipped clean through. This being said, how tough is sternum and front of the rib cage on deer sized animals?