In some ways, it's a cardinal sin. In other ways, it's understandable. There's a whole world of difference between tweeting between sets to try and inflame your friends' jealousy, and holding your gargantuan phablet above your head for three or four songs at a time, blocking the view of those behind you, and capturing video that is so low quality that no one will want to watch it. Ever. You might wish you'd never even bothered to shoot it in the first place.
What's OK according to your personal smartphone concert etiquette? One quick shot as the headliner comes out on stage? No pictures, but texts, tweets, and Facebooking between sets? Unconditional and violent death to all phone-wielders?