I dunno, this can't really be that wide spread. I've used Uber maybe 40 times and never had a problem... other than one woman who reeked of old lady perfume. Most have been pleasant to ride with.
The thing is, you get their name, make and color of car/vehicle, their tag number, driving record, etc.
The tag thing though, that really is the crux. It directly ties the driver to a car and usually a place and if someone really wants to find you they will find a way. The retaliation could be on a big time scale so I don't see this being a common day thing.