Man vs Wild is hosted by Bear Grylls, an ex
British special forces guy who's "climbed mount Everest etc etc." He is followed around by a camera crew that films him demonstrating the survival skills you would need if you were stranded in that week's destination.
Survivorman is hosted by Les Stroud. From what I can tell, he is just an outdoors-man who must have worked at one of those stores like REI or Whole Earth for a really long time. Unlike Bear, Les hauls all the camera equipment with his gear and films himself. He has no film crew following him around and helping him build stuff off camera. He is just alone in the wilderness for 7 days.
I have had the debate with a lot of my friends before about whether Man vs Wild is fake or not. I used to say that it's real but the more I watch, the more I realize how much help he has to be getting. He still eats all the gross beetle larvae and drinks his own pee etc, but his upbeat attitude and healthy look makes the fact that he is in the desert without water and food all day seem improbable. What Man vs Wild does have going for it is Bear's accent. If you know what I'm talking about, lets share a giggle. If you don't, you need to watch Man vs Wild.