Ubiquitous vehicular (and ground based) video has serious implications for privacy (as well as distracting drivers) but the ability to record unexpected natural phenomena such as tsunamis, tornadoes, and meteor strikes makes for some remarkable videos. These video recordings also make it possible to reconstruct crimes in ways that we never imagined a few years ago.
I thought a part of the reason for these cameras was to protect the drivers from corruption? I do think that they are a great idea but it is a two edged sword: could be used to help or prosecute the driver.. Anyway, as long as there is no viewing screen to distract the driver I think they are a great way to document the unexpected.