Originally Posted by mander

This is wrong, I think. Once your tire has broken traction with the road it's lost most of its stopping power. Most of your power in a skid comes from the point just before the tire loses traction. So, other things being equal a series of skips will be better for slowing down in a hurry than a straight skid over the same distance. It's basically a very low tech version of ABS. Of course, adding a front brake makes a much bigger difference.

Disclaimer: I'm not a real bike physics nerd, I just play one on bikeforums... someone may correct or add to what I've said here.