Usually when a stranger gets behind the wheel of your car, it's more a situation for the authorities than General Motors. But with the impending nationwide rollout of RelayRides' P2P car sharing program, owners of GM vehicles will soon be actively looking for complete strangers to take a spin at their wheels in exchange for cash. The startup, backed by venture capital from Google, launched its unique rental service two years ago in Boston and San Francisco and is now poised to expand that reach to about six million OnStar subs with an upcoming smartphone app. Admittedly, it's a bizarre, though potentially lucrative concept, as those who opt-in and open their driver-side doors to randoms could net anywhere from $250 to $1000 per month, while renters only have to cough up about $5 to $10 per hour. It's a tough sell when compared up to the more traditional, well-established likes of, say, ZipCar, but if you're keen on sniffing that previously-owned car smell, this should be right up your alley.