Backlinking, Sort Of
A key complaint of Old Hypertext Guys about the web is that the links should be bidirectional. Of course, a pair of <a href="" id=""></a> elements that point at each other make a bidirectional link, but that requires edit access to both of the pages containing these a elements.
For example, this link displays pages that link to this weblog posting—or it will, once Google's crawler finds the link I created from my web site to this page. For an example that shows more pages linking to a page with one of these links, see Micah Dubinko's Pushbutton Paradise in Print, near the bottom.
I was hoping to find some parameter equivalent of Google's "I'm Feeling Lucky" option to add to the link so that clicking it would take you directly to the top Google-ranked page that links to the page with the link you clicked, but I couldn't find such a parameter, so it remains an "indirect" backlink, taking you to a list of pages that link to your page. (My research into an attempted direct backlink did turn up a great reference to Google parameters, and then of course there's O'Reilly's Google Hacks, a book full of neat tricks.)
As Nik Barron pointed out when I mentioned this trick on a hypertext mailing list, it assumes that the system has access to the web and is known to Google. In a closed system with no connection to the public internet, it won't work, but if that's the case, a link manager for the closed system that tracks links and enables backlinks (and much more) would not be difficult to build.
I've recently discovered another nice use of this trick. If you bookmark it by right-clicking "this link" above and picking "Bookmark This Link" (or, from IE, "Add to Favorites") you'll put it on your bookmark pull-down menu. This gives you a quick and easy way, while looking at any web page, to see what other pages link to that page.
Bob DuCharme (http://www.snee.com/bob) writes the Transforming XML column for XML.com. He's written four books and dozens of on-line and print articles about information technology without using the word "functionality" in any of them. Bob's weblog is dedicated to linking-related topics.