I'd actually also be willing to donate a little for the development of such a cool tool.
It's not open source yet, but I might open it up in the future. There's a donate link hidden away in the About page. Any donation would be much appreciated, and would help with the server costs (it needs a huge amount of RAM to store the whole planet's data).
I for one would positively crave an option to seek out hills. I've always found London far too flat for my taste.