I have no real issue with people using any equipment like ipad, headphones etc, as long as they pay attention, and to be fair i'd say the majority are paying attention even it seems like the opposite.
It gets so tedious though when in every hand, the same villains who are listening to their music miss what is happening totally, sometimes they'll try and call the big blind when they missed the mid position raise/reraise, then they sit their looking confused and saying 'what just happened/how much is it, is it on me' etc, ultimately slowing the action down, and we all know how slow live poker action is at the best of times.
Or worse still if the dealer keeps having to wave in their face when its their turn and they are just staring down at their ipad/phone etc with music on too loud and seemingly not too bothered with keeping the game flowing. Then just to annoy me even more they tank for ages and muck!