I'm always wary of reading anything in cars, and just cars, since other vehicles don't trigger it any. I've been on boats and planes, no problems. Games won't bother me as much, but I've gotten nauseous while reading before so I try not to do it much.
Although I've found out it's not so much the motion involved that gets me. It's any glare around. If there's a glare involved somehow (such as off the pages of a book) along with that motion, then there's a chance I'm going to feel sick, even if only slightly. I remember driving along with my dad one time (I had to go with him to drive him back after his doctor's appointment), and the glare off the road was enough to make me feel extremely sick after we arrived. Granted, it was a rather strong glare, but...it still happened.
So yeah. Fun.