Mobile phones even on silent can be a nuisance in concerts: I once sat next to a couple who spent the whole concert texting on their brilliant blue flashing screen: very distracting in a darkened theatre! Why did they bother going, I ask?
There does seem to be a sort of inverse proportion law that the more informal the night is perceived to be, the more it's "okay to talk". As for those folk who think it's Ok to get out of their seats, clatter and stamp across a boarded floor, push the door open forcibly, all on their way to the loo IN THE MIDDLE OF A SONG, and do the same in reverse on their way back from it............sadly we now have to ask our MCs to remind folk to wait to the end of a song before entering or leaving (shouldn't have to if they had any manners, sensitivity or consideration for others). On one occasion I was waiting outside the door with my arm across it, only to have it nearly broken by some bad-tempered loud/foul-mouthed drunken woman determined to blast her way back in.
As for classical concerts, it seems there's a band of people who now think it's fine to talk all the way through the overture: NO, it's actually part of the performance!