I finally caught Les Stroud's Survival Challenge this afternoon. That's the one where he takes of bunch of NHLrs and challenges them to survive 24 hrs in the bush, very much like the kids on Surivive this but only a day instead of longer. I don't want to sidetrack this discussion by talking about the show, but an interesting thing happened at the end of the show. They sent all the groups out with a Spot2, but they were one unit short so that group had only their maps, compasses and cel phones to rely on. In Les' words, from the SPOT Adventures website:

"...something went wrong with Brad May’s group. They were extremely late. In time I sent in one of the local guides to find them as he was well experienced in the bush and knew these lands like the back of his hand. But on his way to trying to find them he noticed that his own compass and gps were malfunctioning. Something was up with the magnetism in that area and it turns out theat Brads team was having the same trouble. This problem sent them off in the wrong direction into what could’ve been thousands and thousands of square miles of just bush. With a small bit of luck on their side, just moments before they were to take a wrong turn, the guide fired a shot in the air and they heard it."

Another vote in favour of carrying a PLB or SPOT of some sort.