I learned from inside sources at FedEx Kinko's that the majority of their money comes from people shipping illegal drugs. They're like Tor nodes for smuggling. I'm wondering how Uber would adapt to that: "We see that you are at the mall. Your neighbor is expecting a package from the creepy lookin' dude at the muscle mass kiosk. So hey, we'll give you a $300 credit. C'mon, ramen breath!" Yeah, this'll go well.
I'm guessing this will work better for those hardware store pickups and cupcake deliveries than prewraoped packages between two people. There are services dedicated to running errands already (I think it was called task rabbit?) and combining a service like uber with an errand boy seems like a good next step. There will hurdles to overcome of course but it may work out. /cc mk