My understanding of zimride/lyft is that they're more about arranging carpooling than acting as professional taxi service.

Does Lyft let random people sign up to work as gypsy cab drivers? If so, I think that's insane.

Zimride arranges carpools for long trips, but Lyft is pretty much just an Uber clone with private individuals operating their personal cars. There is some vetting but no insurance or anything as far as I know.