My understanding is that for private cars, they've said they don't log this data without consent (and a signature). I don't know whether it's available to the user - that'd be neat for sure.
The Tesla logged data is definitely available to the user -- there are apps available to help the user interpret/exploit the results:
http://www.teslamotors.com/it_CH/forum/forums/model-s-iphone...
> After a negative experience several years ago with Top Gear, a popular automotive show, where they pretended that our car ran out of energy and had to be pushed back to the garage, we always carefully data log media drives.
Off-topic, but I'm curious whether they log this data for all cars, and whether this data is available to the driver (even if they need to work a bit to get it or ask for it)