I personally hate the motion controls for MK7, you don't just tilt the controller you tilt the screen with it. This type of thing is better off on the Wii, not a handheld!
I've only used it a few times to try it out, I prefer looking from behind the character in a racing game because I can see what's going on and I can judge bends easier, whereas you can't when it's in a first person perspective.
Use it if you want, but I can't stand it, it's far too annoying to even bother with and although the 3D helps to judge the bends better, when you tilt the thing you might as well be blind because the screen goes double... that motion control idea was kinda retarded.