I actually would prefer if there were less applause in the middle of shows, so I definitely don't think it's rude to not clap during the show. It can really break up the flow. It's kind of like how many of us feel about standing ovations - if it becomes standard, it doesn't really mean anything. If people clap after every song, then they have to clap even longer when they are really blown away by a performance.
I'm not saying it's inappropriate to show your appreciation to a performer during the show, but I certainly wouldn't not date someone because they choose not to do so.
Zack
Pass it on - Take a kid to a show.