Anybody ever use a hidden camera, such as a "nanny cam"?

If so, what were you experiences with it - video quality, etc?
Did your camera also record sound? And if so, how was that quality?
If you're willing to say, what make/model was your camera?

(And note: I'm not asking about the morals/ethics nor the legality. Those are important, but not what I'm interested in.)

Thanks in advance!