I stopped playing games about 10 years ago, but thought I would come out of the break to play Portal... I did, and was very saddened to find that I just couldn't play it because it gave me really bad motion sickness and headaches. The nauseating feelings kick in after just 60 seconds of gameplay (and no, not just when going in and out of portals -- even when I'm simply walking around without making portals the headaches come in).

I hope more research is done on this, and some solutions are found, because I really want to finish playing Portal. :)