I have putted looking at the hole. I tried it again the other day on some longer putts. Distance wise it worked pretty well for me. Ironically for me, although I can putt really well on the practice green using this method, I can't take it to the actual greens, on shorter putts, for a better score. I think the reason it does not work well for me on shorter putts is the way I practice rolling a straight putt. I will lay a dime on the green about 18" in front of the ball, on a level part of the practice green. I then practice rolling the ball over that dime. If I can hit that dime, I have rolled a straight putt. By looking at the hole on the shorter putts, I don't have that spot in front of the ball to roll it over.
The other problem is that sometimes the hole is not the actual aim point because of the the green not being level between the ball and the hole.