I don't see how tweeting about the symphony while watching the symphony is a bad thing. you are reflecting on/discussing what is going on around you.
how many people here have regularly attending the symphony? My wife went to IU music, played in symphonies for years, and we have been BSO season ticket holders for years so i speak with some knowledge here.
The symphony does not require full attention.
why do they give you the huge program full of info on the works, the performers, the hall, etc? to give you something to do. check out how many people are flipping thru it during the performance.
we usually zoom out immediately at intermission to grab a few drinks (clearly not a help to sustained attention), after having a few before the show as well.
i can easily listen to a work and pound out a few emails/tweets if i wanted to.
that said, i'm not a fan of many of the contemporary works (legend of zelda, etc). sorry, just not my thing. imho. if it brings others though, no nuts.