The question is, is it appropriate - surely? When it's a fiddle, or designed to cover up ineptitude that's bad. However music and movies do it for mostly production reasons. My absolute hate though is when they try to pass it off as sung or played live. On UK TV over the weekend was X-Factor, and Cheryl Cole (or whatever she is called now) was obviously miming for two reasons - one, way the fact she was full on dancing. After the thing finished, they tried to interview her, but she could hardly draw breath, which was a giveaway that during the dance she was miming, but two, she was simply a lousy mimer! Lip sync random throughout. When people started to use Facebook and twitter to comment on it, their response was to admit it was pre-recorded because of set and costume problems - but to still insist it was sung live, which watching it, only an idiot would believe. My band has lip synced to our tracks simply because we had no production option to do it live. Multiple takes had to have a consistent tempo and sound or the edit wouldn't have worked. I can live with it, and if asked if we were miming, we just say of course! Feature films have dubbed their dialogue for years - nobody notices when it's done properly.
With bands - videos often look horrible when everything is miked and cabled. It's amazing how many drums are miked perfectly in the videos with not a mic in sight? That's life, I guess.