I've seen it used mostly in civil court cases. Usually when there is a death or significant bodily injury. They've been on cars dating back to 1997, and their use has been relatively rare given the amount of crashes that have relied on the data.
For Nissan/Infiniti specifically, EDRs are only in 2013+ models. Complete list here:
http://www.rimkus.com/uploads/pdfs/E...a_Recorder.pdf