It also helps to have clergy who actually sing along. Our rector just belts it out; usually he gets the notes right. His enthusiasm is infectious, and the congregation sings more than any other Episcopal church I've been a part of.
Mark, I can relate to your frustration. Lately our director has taken to starting practice bang on time, even if only two people are there. He has just lost patience with the prima donnas who want to hang out in the narthex and socialize until the last minute (we have practice right after the Sunday morning liturgy). I do try not to second-guess our director. I wouldn't want to do what he does.