A lesson of sorts for me today: I was reading through a few old posts on this site and came across one that referred readers to a link in the left-hand column. Of course, there is no left-hand column anymore. I think that was removed one or two site redesigns ago.
The lesson is that the Web is infinitely malleable. All the content can change shape, context or form instantly, making such old-school paper-like references meaningless. I supposed its a Web design lesson too; never refer to another part of the page because you can’t always guarantee that part of the page will be there. Prefer the hyperlink.