The six biggest "gig gripes" recently identified by 6 Music listeners - mobile phone usage, touts, talking, admin fees, cloakrooms and access - probably won't come as much of a surprise, though the resulting article is nevertheless worth a read for its consideration of possible solutions.
Talking through sets (particularly quiet ones) and exorbitant admin fees are two real bugbears of mine, but I'm slightly more conflicted as regards mobile phones. On the one hand, it's immensely irritating to have your view blocked by someone filming a show when you've actually paid money to be there in person - but, on the other, I do regularly enjoy watching fans' footage of gigs on YouTube (which was presumably gained to the annoyance of the punters nearby). While I don't actually film shows myself, I guess that makes me a bit of a hypocrit.
Touts are an obvious scourge, but I disagree with the suggestion that tickets should have names and photos printed on them - after all, this would discriminate unfairly against people who have bought tickets in good faith but then find themselves (for whatever reason) unable to go and simply want to recoup all or some of the money they shelled out. The last thing the live music scene currently needs is another reason to make people hesitant about buying tickets.