When we went last December I rode MS. I thought it was a good ride, but not one of my favorites. The first time I got in line to ride it. after listening to all of the comments on the board, I had worked my stomach into knots before even getting on the ride. I ended up feeling "off" for about 4 hours afterwards.
Several days later I decided to try it again (wondering if I was crazy for putting my self through it again). I forced myself to remain calm, stare at the screen, ignored all the working of if you are prone to motion sickness, etc. I handled it just fine. I actually felt better than I do after riding Body Wars or Star Tours (They make me feel a little "Off" to but only for 10 or 15 min. at the most).
So I would recommend if you are going to ride it try not to think about if you will get sick or not. I think it is a ride you should try to ride at least once or twice. At this point I would ride the ride again maybe not every trip but more frequently than body wars.
Jeremy