It basically lets you string together wireframe sketches into prototypes that you can tap though on iOS devices.
I’ll let you know what I think after I try it — whether I will be using this for my own projects or will continue to put these together in XCode. I will also try doing this using IDEO’s LiveView over a webcam video pointing at a stack of paper prototypes (which would better lend itself to on the testing and inventing in realtime using the Wizard of OZ technique).
If you have experience with any of these methods of prototyping, please tell me about it.