Personal car-sharing is a new twist on auto rentals Reporting from San Francisco -- Emily Castor's metallic gray Honda has been driven by dozens of people she's never met. They treat it well, pay any tickets they get and do the dirty work of finding a legal parking spot when they return it to her neighborhood near Golden Gate Park. Castor, 29, is pulling in hundreds of dollars each month through one of several personal car-sharing companies that have burgeoned in the Bay Area over the last year. For $8 an hour or $45 a day, renters can climb behind the wheel of her Civic. Insurance is included. The Bay Area has become a laboratory for personal car-sharing, as well as the broader "collaborative consumption" movement. Rooms in private homes, outgrown children's clothes, parking spaces and more can be rented, borrowed, bartered or gifted through a burgeoning number of Web-based ventures. Unlike companies such as Zipcar that finance and maintain a fleet of vehicles, personal car-sharing networks are possible wherever enough owners and renters sign up. There are nine operating in the U.S. - at least one of which has plans to expand in Los Angeles - and 25 globally, said Susan Shaheen of UC Berkeley's Transportation Sustainability Research Center. For renters, the main advantages of the arrangement are cost, convenience and variety. Lisa Gansky, author of the book "The Mesh: Why the Future of Business Is Sharing," has tracked more than 5,000 companies around the world that focus on access rather than ownership. Both a renter and investor in RelayRides, Gansky said that although she can't justify owning a convertible, "I'd be happy to pay to have it on a weekend. Likewise, I certainly don't want to be driving the Exxon Valdez, but having an SUV for a half-day of hauling is helpful. The business model was born one bone-chilling day in 2008, when Shelby Clark found himself bicycling through the Boston sleet to get to the closest Zipcar. As he pressed on, he recently recalled, he noticed how many cars were parked along his route, just waiting to be used. Clark launched RelayRides in the summer of 2010 and by the end of the year had moved the headquarters to San Francisco. The company Castor uses, Getaround,debuted in the Bay Area in May and now operates in San Diego and Portland, Ore. Wheelz - a campus-based company - rolled out at Stanford University in September, expanded last week to UC Berkeley and plans to begin rentals at UCLA and USC within the month. Another venture, JustShareIt, has added boats to the mix. Vehicle owners typically set their own rental rates and the companies take a percentage of up to 40%, a good chunk of which goes to cover insurance. The companies vet driving records and set standards for the vehicles they accept. Getaround asks renters to fill the tank, while RelayRides and Wheelz track mileage electronically and charge users for gasoline accordingly. A California law that went into effect last year has guaranteed additional owner protections: Insurance carriers can no longer drop customers for participating in car-sharing networks. Evolving technology allows renters to access vehicles without a face-to-face key swap. But for some companies, the process has not always worked smoothly. Zachary Worthington put his Mazda Miata MX5 on RelayRides in October and has earned $700 - enough to make his final two car payments. But Relay's remote-access feature has been balky in his North Beach neighborhood, leaving Worthington and his renters unable to turn on the ignition. As soon as he gets the Relay kit removed, Worthington said, he will switch to Getaround. And although renters have left Cheetos crumbs in his Miata, the arrangement doesn't "leave a bad taste in my mouth," Worthington said. I knew this was a new thing and I really think it's cool to transition into more of a sharing economy. Another car owner, Emmanuel Zamora, has had problems with Getaround's equipment, which allows renters to unlock the car through a smart phone app. Instead, he put a lockbox on the door of his Mission District flat so renters can get the key. Both companies say they are working on improvements.