You can rent this penthouse in Rio for $258/night on AirBnB

You hear a lot these days about the sharing economy and collaborative consumption, especially if you spend time in northern California. I spent last week in San Francisco, where people told me about AirBnB, which allows people to share their homes or apartments with visitors, RelayRides,  Share My Ride and getaround, which allow people to rent their cars for a few hours or days, and ThredUp, where parents buy, sell and share children’s clothes, toys and books. Meantime, Prosper.com and Lending Club connect people who want to lend money with those who want to borrow. With peer-to-beer lending, who needs Citi or Bank of America?

Last year, Fast Company published a thoughtful and well-reported overview of the sharing economy by Danielle Sacks under the headline: “Thanks to the social web, you can now share anything with anyone anywhere in the world. Is this the end of hyperconsumption?” More than 3 million people from 235 countries have “couch-surfed,” she reported, and more than 2.2 million bike-sharing trips are taken each month.

Many sharing websites, like Freecycle and Couch Surfing, are nonprofits. Seattle and Berkeley have tool libraries, where people can borrow a lawn mower, power saw or drill. But other sharing ventures are business. Some analysts expect the sharing economy to generate real money, Fast Company reported:

Gartner Group researchers estimate that the peer-to-peer financial-lending market will reach $5 billion by 2013. Frost & Sullivan projects that car-sharing revenues in North America alone will hit $3.3 billion by 2016.

I’ve always liked the idea of sharing-–hey, I paid attention back in kindergarten–-because of its obvious environmental benefits: The more we share, the less stuff we need to own. But I’ve been skeptical of the claim that the sharing economy would end–or even slow down–hyperconsumption. My week in San Francisco made me less of a skeptic. This idea just might spread.

Partly I’ve changed my thinking because of my own experience. For the first time, I stayed in an apartment that I found through AirBnB. Because I planned to spend six days in San Francisco, staying in a downtown hotel struck me as unappealing. I liked the idea of exploring a neighborhood, making my own breakfast and saving a few dollars. So I found a studio in Potrero Hill for $140/night that I rented from a woman named Kepa Askenasy.  I chose it in part because Kepa was rated a “SuperHost” by Air BnB and had about 70 favorable reviews from renters on the site. It’s the top floor unit, below.

My digs in San Francisco

I felt some trepidation as I boarded the plane for SFO-–this wasn’t as predictable as staying at a Marriott, or at one of the Joie de Vivre hotels in SF, which I like a lot–-but everything worked out really well. The apartment was small but comfortable, and Kepa kindly provided maps, neighborhood guides and her own advice on local dining and shopping.  I explored Potrero Hill, enjoyed a long walk to downtown for one meeting, got around on buses and the Muni, went for a run with my pal Adam Lashinsky (buy his new book!) who lives nearby and hung out at Farley’s, the local coffee shop.

The peer reviews on AirBnB took a lot of risk out of the transaction, for Kepa and me. She got paid in advance. I was reassured by her ratings. Afterwards, we rated one another, to guide future renters and lessors. She told me by email:

Airbnb emphasizes customer service, and accountability on both sides of the equation (host/ guest) through their transparent review process. It’s been exceptionally easy to handle the transactions. My guests seem to be happy with their side of the deal too.

Should Marriott and Hilton be worried by AirBnB? Probably not, but it’s not going to help their business.

Later in the week, I had lunch with Beth Trask of Environmental Defense Fund who told me that she’s renovating a home in Berkeley. And, yes, when she needs tools, she visits the tool library. She told me:

The Berkeley tool library is a real community gem.  I’ve borrowed everything from rakes and hammers to drain snakes, sanders and power tools.   The crusty old guys who run it love to tease me — since I never know the right names for the tools I’m looking for and they usually have to explain them to me – but they always help me out.  I’ve saved so much money and time, and have learned a lot about tools along the way.

On a visit with Net Impact, a great organization of MBAs, young professionals and college students who want to use the power of business to change the world for the better, several young staffers told me that they thought the sharing economy was a real phenomenon among younger people. Liz Maw, the executive director, was planning to rent a car the following day from getaround, but was stymied by a couple of glitches. But others in the group had used car sharing services, which provide peer reviews as well as insurance. Most cars, it turns out, sit around as much as 90% of the time.

I’d readily use AirBnB again, and I’m prepared to try car sharing. I’ve been using Freecyle for years [see my 2007 Fortune.com column, The amazing Freecycle story]. It strikes me that free or government-backed sharing programs, like Capital Bikeshare in Washington, D.C., function as gateway drugs for people who have forgotten the lessons they learned in kindergarten. They can move from there to Zipcar and from there to sharing their own car or apartment, and borrowing from others.

Lisa Gansky, an entrepreneur and author of a book called The Mesh: Why the Future of Business is Sharing, is the leading evangelist for the sharing economy. In a manifesto called Six Reasons Why the Sharing Society (aka the Mesh) Will Trump the Ownership Society [PDF, download], she has this to say about the environmental advantages of sharing:

Barring some miracle in space, there’s only one planet for us to inhabit. And by mid-century, roughly three billion more people will join us. With this math, it’s not hard to predict that businesses that figure out more efficient ways to use the earth’s resources will thrive. Also, urban areas will inevitably become more densely populated, which really favors the sharing economy. If you’ve got more people in a neighborhood, it’s easier to increase the number of bikes, tools, local farmers markets or clothing swaps you can offer. You can also make your offers more convenient—more shared cars in the lot or on a nearby street. Density deepens community and creates demand for shared products and services. Owning a car outright, on the other hand, becomes a bigger and bigger expense and burden to maintain and park.

Very cool.