For starters, just to clarify, peer-to-peer car sharing differs from traditional car sharing services such as Zipcar in that it allows people to rent out their own vehicles to others at rates set by the car owners themselves, and would theoretically siphon people away from buying new autos.
Hence the question about GM's recent funding for RelayRides, one of a handful of peer-to-peer car sharing services in the U.S. According to Hamilton, "what matters most is that more people are driving around in GM vehicles, whether they own them or not."
The primary obstacles for peer-to-peer start-ups such as RelayRides aren't getting backing by institutional investors (which include Google Ventures, August Capital, and now General Motors), it's much more psychological.
As Hamilton writes, "The big catch, of course, is whether Americans are really comfortable renting their personal cars to strangers. 'Some people by nature don't want to share anything,' concedes Bob Tiderington, GM's Manager of Business Initiatives, the unit that partnered directly with RelayRides. But the rise of collaborative consumption, in which people rent or lend everything from a hammer (at borrowtools.org) to a cocktail dress (at renttherunway.com), suggests that enough people are comfortable with the idea to make the business model work."