In reply to UKC Articles:
Placing ice-screws with a slight downward angle can be a good idea in hard, uniform, compact ice where the thread will hold well. In anything else - air pockets, snow-ice, melting ice (as per this video) - ice-screws should NOT be placed head down. As you often don't know what you're placing your screw into, it's usually best to play conservative and go for a horizontal placement.