Doug Bowman has a nice post about using unordered lists for site navigation, then using CSS to style them any way you'd like (horizontally for instance). I think it's a good idea and makes sense, structurally, in the code. Going a step further, why not use a definition list to do the job with a <dt> of "Navigation"? This will label the list for non-styled viewers (and readers), yet it can be hidden in the styled version using #nav dl { display: none; }. I think it makes sense for navigation lists to be titled -- especially when there are additional lists for sub-navigation or other header elements. This site now uses one <dl> for the nav, then hiding the definition title.