Firstly, Happy B-Day, Mister Tealeaf!
Depends on the group. I've played or DMed a few and it's always unique. Lighting changes tend to work better with groups that are more role-play heavy and less rules conscious (or know them very well). As long as you don't have a lot of paperwork, looking up rules, and the need to see dice, you could even turn the lights off entirely.
Music, too, can be a distraction, though some of the groups in which I've been enjoyed Mannheim Steamroller, Jetro Tull (he's good!

), Celtic Music, Madrigals, Gregorian Chants, or things like that but always softly in the background.
Haven't seen much on the way of costumes unless at games at GenCon. I did know a guy who always wore a heavy cape, in the winter, instead of a parka or something. He didn't wear it inside the house, though.
Anyway, I hope you read this tomorrow and are out having fun tonight!
