Well a similare topic started a 300 post debate over at bicycling.com.

Anyway what I get out of it is that if you are climbing lead with the heel all the way around the stroke. If you are spinning fast or just plain going fast the heel is held up and you point your foot down slightly.

Well hey, thats what I usually do anyway. I could be wrong. But when I climb I naturally find my self leading with my heel, while spinning and speed like above, even on hills if they are short enough.