I love the idea of PianoCheetah, when I get my piano out of storage will definitely give it a whirl.

I tried looking at the demo video to get an idea of what it does, but (almost literally) couldn't follow along to save my life!

To get more testers etc I would 100% focus getting really good youtube videos out there. You don't even have to make them!

When I hear about a program like this, all I really want to know immediately is what it feels like to play with it. Do a couple of "Let's Play" style videos, show us how much fun you have playing piano with this tool. It will sell itself after that :)