The problem with touch-screen keyboards is that they offer absolutely no tactile feel - you have to look to find home row, and you can't feel the keys under your fingers. They just don't allow one to type as fast.
This one looks a little smaller than the standard keyboard as well. My netbook has a 92% sized keyboard and it is harder to type on also. But at least I can feel the keys under my fingers.
I don't like the touch screen on the iPhone either, though I do like it's other capabilities. Of course, even with a proper keyboard, it is way too small to allow fast typing.