I installed my two brother's racing slip-on this past week and wow, does it sound good. I'm very happy with it. I made a little how-to on the process and also added some video clips of before and after. I figured I would post the link here for anyone interested in doing it for themselves.
http://www.wootbike.com/articles.php?article_id=5
http://www.wootbike.com/articles.php?article_id=5