I sang in a college choir a number of years ago, and we did some great
choral works, Bachs BMinor mass, Carmina Burana etc. The choir was made up of students and community members. At one performance a student had an earphone in one ear so he could listen to the hockey game at the same time.

Yes Id definitely say its poor manners to bring a gameboy, or a tv to a concert. maybe its a stretch to say theres an overall decline in manners - but at the same time it shows how much people are obsessed with technology and cannot seem to appreciate the real experience of listening to music, or for that matter having a quiet moment without
any techno intrusion - whether its a cellphone, ipod, gameboy, tv (all those are converging anyway)

Also it sort of depends on the venue, if the performance is in a pub
as opposed to a concert then people probably should be able to talk.

Was a quiet audience always the case? I seem to remember reading about operas and even plays and vaudeville in the past where people brought food and drink and came to socialize and make business deals.