I'm using frames to create side and top menus, specifically for navigation and advertising. I know it's not the best way to go about it, but without being able to nest catagories under each other, it was the only solution I could come up with considering I have hundreds of boards, with more to add. If you'd like, take a look at it and tell me what you think (
http://www.yourvacationdreams.com). I don't think it creates too much of a crowded look, but I haven't received a lot of feedback yet as it's still very new. The "lean look" might be an option that could be of benefit to my type of interface.
http://www.yourvacationdreams.com