What are your thoughts on this: say you have a breadcrumb trail on all of your pages (Home » Boxes » Cardboard Boxes). Would it make sense on the "Cardboard Boxes" page to hyperlink the last part of that breadcrumb trail? (in other words, a page that links to itself).. Is it worth doing this to create more internal links, or would it wind up being a problem?
I wouldn't link to it. Not only could it be possibly considered an attempt to manipulate the search engines, but it could also confuse your visitors as well.