I've shot one deer in the head in my 13 year hunting career, it was a doe that I had shot in the spine. It went down, but was still trying to drag itself with its front feet. I slipped up about thirty yards from her, and the only thing I could see over the brush was her head, so I let her have it. Bullet went in her left ear, exited out the right. Quick and painless. In that situation at least. I wouldn't try a head shot under normal hunting circumstances.