As you might expect, the rental service only includes GM vehicles, like the Chevy Volt hybrid EV or a gigantic Escalade. Prices start at $8 an hour for cars and $14 an hour for SUVs. In total, 60 cars will be available at 30 sites throughout the city with a focus on the Financial District, SOMA, Embarcadero and Mission District.

In addition to San Francisco, Maven is currently available in Ann Arbor, Baltimore, Boston, Chicago, Detroit, Los Angeles, Washington DC and New York City.

Like ZipCar, City CarShare and Enterprise CarShare, the vehicles must be rented and returned to same site. San Francisco doesn't allow car-share full-size vehicles to be picked up and dropped off on the street. So don't expect a Car2Go or ReachNow type service anytime soon from the automaker or any other company. Although the company does say it's investigating that feature.

What Maven does have going for it that other car-share services are sometimes lacking is that after you sign up, the acceptance process is relatively quick. "Usually within a few hours," according to Jeff Shields, Maven's west coast regional director. That said, it could take up to 48 hours.

Once you are a full-fledged member, though, you can use your smartphone as your key, as opposed to the NFC cards offered by ZipCar and Enterprise CarShare. Couple that with the built-in OnStar feature that can help members find a destination and even extend the length of a reservation, GM seems to have created a pretty frictionless experience indeed.