It sounds like you might already know what they are.
What are the true costs?
Another aspect of this that doesn't get a lot of attention is the tax implications. If Uber drivers are technically independent contractors, then Uber may be required to file 1099 forms with the IRS and the income their drivers get paid must be reported to the IRS.
As time goes on, I think a lot of these drivers are going to decide that this isn't such a great deal for them.
Interestingly, I don't think Uber sees this as a long-term venture as it is currently constructed. I've long felt that their ultimate goal is to make money by selling their rideshare technology to taxi and limousine companies all over the world.