Lot of info here, and some pointless arguing. I actually only got in about two hours of work this weekend before the chainsaw decided to quit. Somebody mentioned 2 saws is a good idea, but I've only got one, soooo, I found some alternate projects until the saw gets fixed.
I have cut hanging trees and trees under tension, so I know what released trees can do. That's why I was so wary going into my first time cutting full sized hung trees. most of my short time sawing Saturday was getting a big tree top down on the ground. It had snapped 15 ft up the trunk and the top was on the ground, and the trunk resting on top of the 15 ft stump. I was able to get it down by careful cutting of the top branches. Once the whole mess was on the ground, the saw stopped cutting and so the tree's still down.
As to the video posted, cutting over by head like that isn't going to happen, and that seems a little to dangerous to try. If the trunk slides the wrong way, curtains for the operator. One thing I've learned is that trees can be unpredictable when they fall, or at least very hard to judge correctly.