The astronauts who went to the moon took quite a few rads in the process. I read somewhere, though I don’t remember where so I can’t dig up a cite quickly, that the lunar explorers have shown a somewhat elevated rate of cancer. However, since there’s fewer than twenty of them, it’s not really an epidemiologically reliable sample. I do, however, clearly remember seeing a micrograph of the interior of one guy’s helmet, and all the tiny little spikes that were created when cosmic rays shot through the material.
Re the OP, it’s important to remember just how freakin’ hostile the Martian environment really is. You have an extremely low-pressure environment (0.1% of Earth at sea level, IIRC), temperature fluctuations, cosmic rays, dust that’s as fine or finer than talcum powder, and more. And those dust storms, when they get cranked up, can cover the entire planet for months at a time. Nasty business, really. So we can test devices under most of these conditions separately, at least on a limited basis, but trying to test all of them at once is damn near impossible. Really, it’s something of an engineering miracle that we know what we’re doing enough to get something that works on Mars for an hour, let alone ninety days.
For some background, read Managing Martians by Donna Shirley, who worked on (and later supervised) the rover program that put Pathfinder/Sojourner on Mars a few years ago. There’s a lot of detail about engineers seeking out particular components that match certain specifications, and requesting additional customizations over and above the Earth-standard tolerances. It’s not just a matter of going to Wal-Mart and getting a drill, a camcorder, and a Sony Vaio and hooking it all together. You’ve got custom-engineered battery packs, specially fitted transmitters, high-tolerance wiring, hardened computer memory, lots of moving parts and mechanical bits carefully sealed against the incursion of extremely fine dust, and more, and it’s all got to fit in a bruisingly tiny little space.
Regarding just the dust: The Science Channel had a thing on within the last couple of days where a U.S. Geological Survey scientist put on a space suit and stood in the middle of an artificially generated dust devil, in an attempt to see what might happen if an astronaut on Mars got caught in a dust storm. The surprising thing was that within minutes, a buildup of static electricity caused by all that dust whipping around him and against itself caused his suit to develop a charge, and his visor was quickly coated with blinding dust. And within ten minutes, all of his equipment had failed.
And that’s here on Earth, minus the vacuum, the background radiation, the extreme cold, and everything else.