I get motion sick on everything... and I mean literally everything, like in swimming pools (from the bobbing motion when swimming

) and sometimes even in the bathroom. I am OK in cars, provided I am in the front seat, stay facing forward always, and don't look in my purse for anything... just sit facing forward, looking straight forward. Planes require serious motion sickness meds!
At WDW, I take one bonine every day. It's a different drug from dramamine and I find it works better and makes me less sleepy than the dramamine. I wouldn't dare try the busses, monorails, boats, or parking lot trams without bonine! SO... even with the bonine, I can't do roller coasters, motion simulators (StarTours, etc), and would never consider even trying teacups or AstroOrbiter, Mission:Space (and Goofy's Barnstormer just killed me). I am "OK" for ONE ride on TestTrak or BTMRR. I have to be careful on both Philharmagic and Soarin. I think it's the "largeness" of the screen and the visual concept of moving, even though my body isn't really moving. It's OK- I know to close my eyes when Aladdin and Jasmine are flying through the streets, for example- and if I close my eyes on Soarin when the woozy feeling starts, I am OK. Soarin is funny, though... sometimes it bothers me, sometimes it doesn't, and it's different parts of the show that bother me each time. I also sometimes have trouble being in the middle or lower row... don't like the closed-in feeling from all those feet dangling over my head, I guess.
As a PP noted, it seems to be different for everyone. I wouldn't risk it... I'd take a bonine, or even a HALF a bonine, and know that I'm "safe."