There were a couple of pretty recent threads that delved into different views of this question as well. You may want to check these out for more info:
http://www.swingersboard.com/forums/...ere-watch.html http://www.swingersboard.com/forums/...-welcomed.html
As I commented in those, it's ok to watch but do be courteous about it, be quiet, and be together. It's one thing to sit in the room and enjoy each other while watching others, it's another to just sit there like you are watching tv on the sofa at home.