A rogue in the limelight
Parents of a young student were worried that he was being harassed by his bus driver, so they put a voice-activated tape recorder in the kid's backpack. Turned out they were right. However, Wisconsin state law holds that conversations (though it wasn't exactly a conversation) cannot be intercepted except by police or people working in cooperation with police. So while the driver was arrested and tried, the recording cannot (as things currently stand--there's an appeal in the works) be used against him.
So What?
This type of law isn't going to hold up for long; the technology (mostly cell phones) necessary to record wrongdoing surreptitiously is becoming convenient and ubiquitous, and this sort of situation will increasingly crop up. Citizens won't understand the legal prohibitions--they'll consider them perverse.
A few hypotheticals. I can keep my phone's audio recorder going just after a road accident and pick up the other guy making incriminating statements. Its video recorder (lens peeking shyly out of my shirt pocket) can catch sexual or other harassment (complete with gestures) in the act. And its still camera can document such anti-social behavior as parking illegally in the handicapped zone. Any of these might be the locus of a lawsuit or a police report, and the notion that they'd be inadmissible (for one reason or another) simply won't make sense to the public.
There is progress, however. New York City has announced that it intends to equip both its 911 and its 311 systems to take images from camera phones--so if you do see a violation of a city ordinance (or something more serious) and can get a picture, there'll be a procedure in place to reward your efforts. (Accenture Technology Labs did some work around this idea several years ago.) New York City is a bright spot, but it would be good to see more.
As a practical matter, I don't really care whether people are good on the inside--George Bernard Shaw famously said that if you put a rogue in the limelight, he'll behave like an honest man--what matters is whether people are watched. Ubiquitous personal monitoring has its disadvantages, but it will tend to encourage people--even sadistic bus drivers--to behave themselves.