I've been using Hitch the last month or so, and Sidecar has had the functionality for some time as well. Its cool to see Lyft and Uber offering the service.

IMO, a big win for consumers, because offering more service-level options, and driving down pricing. With Hitch, it usually costs me $9 for what costs $16-22 on UberX, Lyft or Sidecar. Thats a nice savings, even if it takes me 10min more to get home. I could really see mass adoption coming from the service who nails this and provides the option that is better than Muni, but cheaper than individual car service.

Another aspect of this service I wasn't ready for was that the social dynamic can completely change the ride-sharing experience. Its different when you are just chatting with a driver, vs a 3rd or 4th stranger jumping in the car. It will be interesting to see how others react and expectations evolve as it becomes mainstream.