Isn't being an employee unnecessary bureaucracy for a messenger service? If anything, I think Uber is doing a great service here to all parties involved by connecting supply and demand in a low-friction way.
For Uber to be worth its high hype & valuation, it's going to essentially expand these types non-employee situations. That's why I'm "mixed" feeling about this, as I like great UX, smooth marketplaces, & know many people who want part-time work, not full time.
But, I also know many folks who had "decent jobs" (nothing special, but they can raise a family) driving UPS trucks or other things like that.