There are a whole bunch of banned words. There used to be a whole slew of sites that indexed all of the things Microsoft wouldn't let you talk about. Here's an article about it in the Inquirer: http://www.theinquirer.net/inquirer/news/1041509/microsofts-...
Edit: that article appears to be mostly user names. Here's a forum thread to get you started: http://www.amsn-project.net/forums/index.php?topic=157.0