Although I am naturally wary (Paypal seeming to be one of the most hackable transaction systems out there) it's about time they did this. If it's done right, and there's enough takeup (especially the scan&pay bit) this could seriously improve (i.e. speed up, the worst part of any shopping is the time it takes!) shopping.
I'll reserve judgement until I see it in action, but I'm cautiously optimistic.