My brother drives occasionally for Uber in Los Angeles. He likes it for the following reasons:
Flexible schedule. He can decide when he wants to work, just by turning on his Uber-supplied phone. He generally works on short-distance fares; transporting people to and from clubs and private parties in Hollywood, and for just a few hours at a time. Or, if he's going somewhere anyway, like the airport, he'll try to get a fare out of it. Drivers can accept or reject any fare they want.
Bonus. He got something like $250 after completing 10 rides; though I am not sure if they offer this perk in every market.
Fun. He's an extrovert who likes meeting new people, and he meets a lot as an Uber driver. He says that a few have invited him to come meet him out later, and that "could have gotten laid" at least once as a result of an Uber connection. (He didn't accept, but he did say that if he were single, this would be a huge perk.)
A reliably worry-free experience. Uber requires a user have a credit card, a smartphone and a degree of tech-savviness. My brother says these criteria tend to weed out a certain class of people; not just anyone is going to use it, even though it's cheaper. And you can see rider ratings, too; easy enough to turn down a fare.
Extra money. It's probably not a great primary source of income, but Uber can help a driver earn extra pocket money if they have the free time and resources. Tipping isn't required, but he said about 30 percent of rides throw him a few bucks anyway.

Here's what he doesn't like about it, and is why he doesn't drive much for them anymore.
Lowered fares. When he first started, he got a certain rate, but Uber reduced it after awhile. Less money per ride means less reason to want to work.
High standards for the car. He told me that in his last inspection, a couple of his tires didn't pass minimum Uber standards, even though they still had quite a few miles on them and were otherwise safe. He didn't want to get new tires right away, so he stopped driving for awhile.
Reduction in referral bonuses. He used to get a certain amount for every driver he recruited, but these went away as well. Another disincentive; like I said, he's a social guy and was a good source of referrals, but lowering referral compensation made it less likely for him to talk it up, and less engaged with the company overall.

From his experience alone, I think Uber is good for a certain type of driver -- someone with a newish, well-maintained car that likes meeting and driving around strangers and doesn't really count on it to provide a real or steady income.