Funny you mentioned this Brian because I've actually thought about this myself. It could be useful if manufacturers included cameras in their cars. Not only for cops but for hit and run incidents or the like. Of course the video could possibly be used against the driver if at fault.
As far as cops, I think a higher percentage of people who crave power and authority gravitate towards that job. Just as a pedophiles would probably want to be a teacher, day care provider or priest.
On the other hand all jobs have some sort of unofficial perks, maybe running red lights and such is theirs.
http://www.spycameras.com/