"When you design for the web, you don't know what software people will use to experience your site, and you don't know what capabilities your users (and their software) have. Flexible layouts and resizable type can eliminate a lot of worst-case usability and design scenarios, but it's still extremely difficult to create page layouts that don't break even if the user increases the type size by more than a few settings." -- http://www.alistapart.com/articles/fontresizing