I know of various ways to dynamically alter web pages' typeface properties via JS/DHTML, or replacing text with Flash-rendered fonts (with sIFR or Cufon). However, I can't find any good examples of dynamically changing the typeface used on a web page depending on user choice - with, for example, the use of a dropdown box or text links (to allow the choice of Arial, Helvetica, Lucida Sans and Gill Sans for example).
I'm sure I've seen this functionality in web sites before but I can't find anything written about it, let alone real world examples! Can anybody point out some good examples / proof of concepts / sites that have successfully implemented this feature?