UV radiation risk:
http://mars.jpl.nasa.gov/science/human/
http://library.thinkquest.org/03oct/01858/text-only/colonization.html
My point exactly. You just do not just send a team to Mars on some Edgar Rice Burroughs dream that it's your God-given right to do so. These individuals are not just in orbit for two years, they're in interplanetary space. No shield from Earth, no nothing.
I'm sorry folks. I do not mean to play the cynic. I'm the first who would want them to get their as ducky as could be. :-)