I'm an iOS dev (approaching a million downloads), and fully half of our support requests are from people who don't understand how the mute functionality on their device works - particularly the side switch on the iPad. It's not a big deal for us since we've got a templated response at this point and it only takes a minute or two for us to send a response, but there are clearly a number of users out there that don't understand how the mute functionality is intended to work.