Each of the techniques described can be used for XSS filter evasion, which was my original intention when developing them. However, learning such JavaScript can dramatically increase your knowledge of the language, helping you become better at cleaning up input, and increase web application security.
http://dev.opera.com/articles/view/opera-javascript-for-hackers-1/
Some great examples of how you can use JavaScript to hack web pages. As a developer you need to know what you are up against, so information like this is invaluable when making sure your web pages are secure.