I found this really fascinating. I also love the simplicity of it. It could be cool if your About Modal had a "Next >" button, and each slide would reveal another critical bit of information, like the one you have above about the actual odds, while the guesser runs in the background. In a way you would be getting paid to learn bitcoin.

Also, wouldn't the odds be far higher of mining a block in your browser than of guessing a private key? My intuition says yes.

Thanks! Great stuff.