I've been thinking of adding a Bread crumb trail on the site. Still debating if this trail should be dynamic (i.e. a true trail of the pages that the user accessed) or a static one (hard-coded on the page itself).
It started in '99 when I started representing the DTD structures that I was working on in a Tree format. When I felt the need to automate the generation of the DTDTree, I could not find a suitable DTD parser ... so I wrote my own. Find it at Matra DTD Parser.