It's hard to say how big and/or profitable the car-sharing industry might end up being when it's mature and stable and all the inevitable regulatory issues are ironed out, but for now as a consumer I welcome cutthroat price wars. In San Francisco I use SideCar almost exclusively, and it seems to be about the same price as a taxi, so it's great to have another similarly-priced option.
What about the recent lawsuits and uber violating transport regulations? My impression (without really following the thing, just reading headlines and a few HN comments) was that Uber can compete with such low prices by not following some legislation there is in the person transport business.
For those that don't know, uberX uses hybrid cars instead of luxury sedans [1].