Navigation
Navigation is to an application as table of contents are to a book. At a glance I should be able to know where I’m at, where I’ve been, and where I’m going. In other words, navigation should answer the question: Where Am I? I see this as being the aspect that we tend to have the tendency of projecting our preferences onto a design. Navigation should also encompass the taxonomy you have for your site so I know the content of your site.