Uber has demonstrated that it can cheaply and efficiently deliver cars to specific addresses (provided it's neither a snow storm nor a national holiday), so now the company is going meta and getting into the delivery business for everything else.

UberRUSH, a new courier service starting today in Manhattan, is an "Uber for things," according to Josh Mohrer, the general manager of Uber NYC. It works like this. You want to send your air mattress to your friend downtown. You request a delivery person on your Uber app. He arrives and picks up the air mattress. You can track him on the phone as he bikes or walks (runs, skates, etc.) downtown. He drops it off at your friend's place and snaps a picture to make sure it's the right location. You pay $15.

It's hard to know how big a deal to make of this. One the one hand, it's an expensive on-demand courier service, which seems occasionally useful, if rarely urgent, and less than revolutionary. On the other hand, you've got people like Aaron Levie, the smart CEO of Box, tweeting: "UberRush is like when Amazon first revealed it was no longer *just* a bookstore. Now comes a steady march toward global domination."

The growth of Uber (for on-demand ride-sharing) and Airbnb (for on-demand room-sharing) and TaskRabbit (for on-demand projects) has been identified as a feature of America's emerging Part-Time Economy. The idea is that Americans can't find work in the formal labor market, so we're sharing our time and possessions with paying customers in a new less formal "sharing" economy. The problem with this idea is that the part-time economy is, by all accounts, a myth. America doesn't have a new part-time jobs problem. We have an old-fashioned shortage of jobs. People have too much non-salaried time on their hands.