The display in the touchpad looks interesting. It would work if the glass on it was matte so it doesn't reflect the main screen and your finger does not stick like on the iPhone (try dragging your finger on the iPhone glass at a flat angle... it sticks).
The dock on the trackpad would be weird though... how does it know if you want to tap something on the bottom of the main display or open an app from the dock? How do pros (who love having lots of icons in the dock) cope with the small space? I don't use the one finger tap on my Macbook at all, I use the button. So you could just make one finger taps to interact with what's displayed on the trackpad.
It could make sense for full screen applications so the HUD or inspector is displayed on the trackpad. For instance, you're watching a video in Quicktime and you have the controls on the trackpad, dimmed to not distract from the actual video. Or you could assign a widget to the trackpad, imagine tile game or webclip. Or how about trackpad Growl?
All the above are mockups!!!!