I didn't do a formal estimate beforehand. by feeling, I underestimated my net earnings. Take home was probably somewhere in the 50/yr range. Keep in mind that I didn't "buy a new car" - I drove with my own car that I'd had since 2010. The whole thing put on about 100k miles; but the car is still running more or less fine, a year and a half later.
My suspicion is that many people who begin driving for Uber overestimate their net earnings and underestimate their deferred expenses e.g. vehicle depreciation and maintenance. If Uber knows this and is taking advantage (with new-driver bonuses, etc...), they're essentially a multi-level marketing company.