[1] My sister-in-law is a public defender, and she demands it all the time and gets a variety of pathetic excuses why "this time" it is unavailable.
If you're ever in this situation just hire a damn lawyer and listen to their advice.
As a hopefully humorous aside, this joke is as applicable to the way "nerds" view the legal system as it is to the way they view cryptography (though obviously in a more metaphorical sense): http://xkcd.com/538/
I've even considered installing cams on my current vechicle.
reading (and watching on Youtube when available) about a bunch of recent beatings and shootings, i think it should be made into a law that a police officer may apply force only when the action is being recorded (by a helmet or Glass-style camera of the officer). Without recording on, police officers should be considered "off-duty" and be subject to regular rules just like any other citizen.
Unless there's a way to reliably stream the data into the central repository (far away from the officer and his/her police department), it won't work.
If the law said "the video has been lost" meant instant acquittal, the video technology would become radically more reliable.