My wife and I are actually looking at it, and thinking. If it is ever to happen, *someone* has to do it, right? We are both intelligent people with advanced degrees, only small families, and no kids...
There's a major question that comes to my mind that the documentation doesn't seem to answer. They ask you to devote 8 years to their training program, during which time you're employed by Mars One. That's cool. But... what if it falls through, and they don't fly? Or if you develop diabetes or cancer in the intervening years, or something? You've devoted, in essence, the time for an entire career to them, and have what to fall back on if it falls through?
I find I'm not all that scared of leaving the world behind. I am, however, not sanguine with having to stay on Earth with no obvious means of support. If they pay you a six figure salary, so you can sock it away for retirement or the like if something goes wrong, then there's no issue. But that's not clear from their current offering.