They had a piece on that in this month's Men's Fitness (UK edition). Apparently this is the secret of the SEALS fitness levels. There was actually a UK gym chain training director expounding on the virtues of the thing. This guy is normally quite sensible.
But they had something even better which I'm afraid will have to wait until tomorrow because I can't remember the link. Then my friends, you will truly understand the answer to all your fitness needs....