From what I have heard from drivers, anything less than 5 stars is bad. Not only with Uber, but with all those companies pushing customers to review their employees. The system is counterintuitive and most people get it wrong at the beginning. Compare what makes you rate 5 stars when you buy a product to your Uber rating system.

However, the think that irks me the most is that rating everyday experiences is just dumb. Most taxi drives will be average and that's it, because we all just want it to be good enough. It's as if my local supermarket made me rate the cashier with 1 to 5 stars. I don't want to do that, because that person just needs to do their job. Anything above "good enough" is unnecessary. Significantly bad experiences should be a "reported to the manager" (or any similar mechanism), filtering out trivial complaints that you'd get in a 5-star scale and getting actual useful information on how to improve the system.

The US restaurant example is funny because the problem is the same. Instead of paying by default fair wages and paying attention to customers that complain about workers, they delegate the 'rating' part to customers, which means that there's no feedback on which they can improve and that their salary is determined by arbitrary people judgements.