Sure, Alistapart, wired.com and alltheweb to name three resize fonts with a styleswitcher. Alistapart has two articles on it, and we've discussed it here before, only I can't find the thread. It couldn't have been more than two weeks ago, and it documented asp [roselli.org] / php [alistapart.com] and js [alistapart.com] versions of css changers/styleswitchers.
I don't know much about it frankly. There were some simple php instructions for random and daily changing styles in the previous discussion, if someone can root it out.
There are other ways to switch stylesheets, as well. Check out thread [webmasterworld.com...] for an explanation of at least one of them.