Cool prototype.  Didn't see it in the demo but I imagine produce would be a significant issue with such a cart/checkout system.  While I'd be tempted to build a scale into the cart I think it might be more cost effective and reliable to have the cart interface with a fixed digital scale and perhaps use Kinect's optics for "produce" recognition.  Beyond this, the biggest technical issue imo is how you build-in reliable/upgradeable shoplifting safeguards without doubling unit costs.  You can imagine how much easier it is to secure the stationary self-checkout registers we have today (simple weight checks, fixed cameras in addition to human attendants).  I hope the project continues to get funded though.

One fundamental change I would make to this prototype right off the bat would be to lose the robotic wheels, place the scanner on the front-edge of the cart (in view of the Kinect optics)...to maximize space for merchandise and even allow customers to immediately bag their items. Green LEDs in the handlebar would indicate to personnel that cart items are cleared to leave the building with the customer.