Interesting idea, but I wonder how well the iPad works with the overlay on when it's not in keyboard mode. The page says you can "swipe through it", but how well does that work and how well can you see through it? Plus it's a bit limiting - you have to be in landscape mode, and iOS 5 adds the "split keyboard mode" to the portrait keyboard.
I think one of the reasons virtual keyboards have become so popular is because they're so space efficient - you have a large screen when you need it (playing games, watching movies, reading) and the keyboard only appears when you need it. Not sure I would give up half my screen space for the limited time I spend typing on it, plus I can always get an external keyboard. If I had one of these on my phone, it would be like having a broken Blackberry.