I went on the ride today after reading loads of threads online about if it was scary or not. I really don't like big coasters and scary rides, but I have been on a few with my girlfriend whilst I have been out in Orlando.
First thing is first- it is NOT horrible or scary or intense at all. It is the smoothest ride I have ever been on, really feels like gliding around. You WILL go up and down and tilt on your back for a very short time (mere seconds) but it is all so smooth it really does not make you feel bad at all. There are no horrible coaster style drops where your stomach turns. Make sure you ignore the videos as you approach the ride that show the riders going upside down, IT DOES NOT HAPPEN. That video nearly put me off.
Probably the only bit anyone will have trouble with are the bits with the videos, which can seem fast, and do simulate flying down cliffs and similar (you don't feel the drops, it is important to remember that) but my tip for this is if you feel scared just look directly up or down, or to your extreme right or left. If you do that you can see the edge of the projection screen and you can tell easily that you are just facing a screen and not moving. I did this on my first time round at the start and then started gradually forcing myself to watch the screen. By the end of my first ride I was loving it and throwing myself into every movement the screen made. I went on 3 times in total and loved it more each time.
My final tip is to just go totally limp and let the floaty ride take you, it is actually really relaxing, it really is that smooth! If you have been on the Simpsons Ride, Spiderman or even Wild Arctic at SeaWorld, you will easily be able to take Harry Potter as HP is so much more smooth (and fun!) It is not jerky like the other rides mentioned, which is what makes me feel nervous.
Hope this can help people who were doing the same frantic research as me! Enjoy!!!