Kotaku posted a letter they received about from a longtime Nintendo fan who also has Muscular Dystrophy. He's having trouble using the Wii effectively.

I'm sure this isn't the last disability-and-the-Wii issue we'll hear about. The idea of a motion sensitivity setting seems feasible, although I'm not sure how feasible it really is given Nintendo's developer tools for gesture detection. That is, I'm not sure if it's possible to easily ratchet down the motion range in software. In any case, developers could certainly capture multiple gestures for different sensitivity levels, although this would require more effort.

In any case, I want to point out that this isn't just an issue of specific disability like MD; it's also one of broad access. There are lots of motion-impairments from age, sports injury, and so forth. Nintendo probably will have to address this issue to cash out the mass market promise of the console.