Last year, Paul English, a co-founder of the travel booking site Kayak--which Priceline bought for $1.8 billion in 2012--looked at his calendar. Ninety percent of his meetings and outings, he realized, were with people in tech or nonprofits. He wanted to broaden his circle. So he started driving for Uber. In his Tesla Model S. On Halloween. After hosting a costume party.

"I went out driving from midnight to 2 a.m.," English says. "People thought it was kind of hilarious that someone dressed up like a vampire was driving a Tesla."

It's a gig English still does a few hours a week in and around his hometown of Boston. "If anyone asks what I do for a living, I usually say I'm an engineer, and then I ask what they do," English says. "It's more interesting to hear about other people."

English doesn't soup up his ride with bottled water or candy. But he keeps a notebook and writes down a sentence about every rider. One of his more memorable passengers was a 13-year-old girl from China, who was visiting high schools in Boston. She hoped that attending one would make it easier to get into Massachusetts Institute of Technology--where English is a part-time instructor at the business school. He mentioned that to her.

"She kind of didn't believe me," he says. "She said, 'Why are you driving a car if you teach at MIT?' I told her I have many lives."

Ubering has helped English understand how service-economy professionals are rated. His newest startup, Lola, which has raised $19.7 million and, as of this writing, is nearing its launch, will have travel agents create itineraries for consumers, who will rate their experience from one to five. At presstime, English's Uber rating was a sterling 4.97. "Being a competitive person," English says, "I wonder: Who didn't give me five stars? What did I do wrong?"

Which is exactly why he set up Lola that way. "I want my agents to be competitive," he says. "Having ratings allows you to say, 'I want to get better.' "