I haven't personally driven but I use the service pretty much 5 days a week to and from work and usually talk with my drivers about their experiences driving. There's a lot of money to be made but you have to be motivated. I've talked to people who set quotas for themselves, for example, one guy I met says he doesn't stop for the day until he's made $200 and he's also in school.
The superbowl will be hosted here next month and he's challenging himself to make $1,000 a day, it sounds ridiculous but that's the kind of spirit you gotta have when the amount of money you make is only limited to how much time you're willing to spend making it.