I can get car sick on almost anything, but on TSM I'm so focused I usually don't notice that I feel a little "off" until it's over, but sometimes I don't feel "off" at all. This is without motion sickness meds.
Most of the time, I try to take dramamine in the AM when I'm going on rides. The only ride I will pass on (at DLR, haven't been to WDW), even with meds, is Star Tours. I have only successfully ridden the ride once and I think it was because it was with someone that was so excited to ride and I didn't want to ruin it so I was super focused.