The other day I needed a ride to the San Francisco airport. My driver was a cheerful soccer mom, 40 years old, in a spotless Honda CR-V. When I got in, she smiled and offered me bottled water. She saw that I had an iPhone and handed me a charging cable. The fare for that trip is usually $50, but this time I paid $32. And no tip was expected or given.

If that doesn't sound like a typical cab ride to you, it must be because you haven't tried UberX.

Maybe you've heard of UberX's parent app, Uber, which lets you summon a car service with a single tap on your phone's screen (now operating in 100 cities). A map shows the exact location of the car that's coming to pick you up, along with the driver's name, photo and phone number and ratings from previous passengers.

UberX, though, is something crazy different. Like its rival Lyft, UberX lets you summon ordinary people in their own cars. People who have some time and want to make a little money.

That was my first real exposure to the sharing economy.

We, the People, have always initiated our transactions by going to a Company. If we want to rent a car, we call Hertz or Avis. If we want to stay in a new city, we call Hilton or Sheraton.

But in the sharing economy, clever Web sites put us in touch with each other. UberX and Lyft are only the beginning.

Airbnb, for example, lets you rent someone's home instead of a hotel. After all, an actual home is often warmer, more relaxing and much less expensive than a hotel; the site has facilitated 11 million nights of lodging so far.

On TaskRabbit, you list grunt work you want done—do an errand, fix a computer, stand in line at the DMV—and fellow citizens bid to do your jobs. Then there's Parking Panda (rent out your garage or driveway). Rentoid (rent out stuff you own). DogVacay (take care of someone's dog).

Of course, Web sites such as eBay and Etsy have always facilitated peer-to-peer transactions. But those interactions have now moved into the real world. You actually meet other people. You enter their cars, their homes and their lives. It's joyous, it's cool—and, for many, it's scary.

Taxi and limo drivers are, of course, furious about Uber and Lyft, to the point of staging protests and slashing tires.

And Airbnb made unwanted headlines in 2011, when a host, on her return, found her apartment trashed. Earlier this year a Manhattanite discovered that his Airbnb renter was hosting a sex party in his apartment.

But clever safeguards can help. Ratings and reviews are essential components of these systems. (I asked my UberX driver, Heather, how she knows that I'm not a serial killer. She smiled and showed me: after I get out, her app also asks her to rate me, the passenger.)

Airbnb now offers $1 million in damage protection for your rented domicile. (The company rushed over to the Manhattanite's place with $24,000, a locksmith and a hotel room reservation during the cleanup.)

The sharing economy was born during the post-2008 financial meltdown, when money was tight; these services are a monetary win for both parties. But now they're coming on strong. They make sense not only financially but environmentally (does everyone need to own a power drill?) and psychologically (why should we pay all our money to The Man?).

There will be more questions to settle as the sharing economy spreads beyond big cities and younger clientele. Who's collecting taxes on all these peer-to-peer transactions? Who's insuring them? And do they comply with all the regulations in their respective industries?

But those obstacles won't last. The “sharing economy” has arrived. And as for me, I'm done hailing cabs. From now on, I'm hailing fellow citizens.