I'm excited for the Surface 2 and will likely get one, but I'm not sure the idea of creating several use-case specific keyboards beyond a standard QWERTY makes any sense. Isn't the whole point of having a dynamic touch screens to enable ANY use case?
It also appears to be connecting via a proprietary connector rather than Bluetooth or USB which means it likely won't work with any hybrids/tablets from other vendors.
Think about it this way: the blade is a second control surface that allows you to make use of the full screen for data or other touch UI.
In audio mixing it's common to have an enormous digital mixing board that's linked up to the mixing software, so that you can fill most (or all) of the screen with the data you're actually working on. Some of those boards have literally dozens of channels with individual sliders, buttons, etc.
It also appears to be connecting via a proprietary connector rather than Bluetooth or USB which means it likely won't work with any hybrids/tablets from other vendors.