... people are even more sensitive to the message that something is bad for you...
Everyone knows that it's bad for your health to smoke but people still smoke. Some negative comments (founded or unfounded) will not stop S3D from becoming popular. My personal opinion on about anything (movie, hardware, S3D, anything) is that it's best to make an opinion from your own experience than through the experience of someone else.
I saw My Bloody Valentine and I thought the S3D was really well done. Personally, I did not feel nausea from watching the movie and I did not notice any ghosting. If I felt any nausea, it was more about the content of the movie (I don't like slashers movies, I'm more of a sci-fi and action movies fan). The only issue that I noticed was that the projector of the specific RealD theater where I saw it was not quite bright enough for my taste. The movie was bright enough without glasses but it was a bit dark with the glasses on.
I think the main tiring issues for the eyes are when there is ghosting, the resolution is too low, the brightness is too low, there's pop-out (except at IMAX3D where the pop-out can be extreme without problems), there's too much separation or there's flicker. As long as those condition don't happen, the experience can be good with minimal side effects.