I don't know if it has changed, but the last time I checked, the statistic was about 10% of people can't use 3D or get disoriented from it.
But it seems a lot more people than that choose not to use 3D even though they theoretically should be able to use it fine without any problems.
I can say that, when I got my 3DS at launch, all the games for it had horribly designed 3D that gave me a headache when playing them, split images all over the place, and when Ocarina of Time came out, it was improved a bit, where only the dark areas had split images.
I had always assumed it was a hardware issue, but it was in fact a software issue, which I found out after looking up the issue on forums. Developers where just making the 3D bad, which would look bad, and cause headaches.
By the time Mario Kart 7 came out developers had apparently figured out how to do it right, as there was only some minor image splitting in very dark areas.
I don't know if others had similar issues that I had with the 3D in the early games the 3DS had, but I can tell you now the 3D works fine with every game I've purchased for the 3DS since Mario Kart 7, and those issues from the early games are gone.
I ask this because an lot of people seem to not really care about Pokemon X/Y, seemingly having poor 3D even in battles, as mentioned by reviews, and the lack of 3D in the over world. Even for games where it's not necessary to have 3D to increase accuracy of movement, it still adds an extra layer to the visuals. To me it'd be like having a 1080p TV and choosing to watch things at 720p.
It's the same confusion I have over people who choose to play games without sound (outside of grinding). Why would you choose to omit something that adds to the experience?
1. The only fool bigger than the person who knows it all is the person who argues with him. 2. They're all complacent sheeple. <==]-<(-_o)>-[==>