If I could make a suggestion for KeyCombiner, I think that having a way to start out as an anonymous user (with no sign up or email confirmation) at first, and then asking users to sign up once they've completed a few lessons would make it even more appealing to try out.
The "Start Learning" button at the top right of your site IMHO should be a bit of a demo mode.
(I know that it's harder/messier to implement a "half anonymous" mode -- this is just a suggestion) :-)