My teacher wife and a bunch of the folks she knows (non-nerds) cover their webcams with stickers or whatever. They’d all love (separate!) kill-switches for their cameras and mics. Plus everyone working in tech I know. So that’s... everyone I know who’s aware their laptops have cameras and microphones.
The problem is, as soon as security expert "Barbara from Facebook" posts something about the NSA still watching you because the switches don't really do anything you're back at square one. :)
Not phones, but for tablets and laptops I think a lot more than just privacy geeks would like a way to know for sure they won’t accidentally transmit video or audio, and would put up with a little annoyance for the peace of mind.