In the age of real-time web crawling, third-party comment services (e.g. Disqus), and a relatively standardized set of "engagement" platforms (Twitter, Facebook), the Linkback standards are probably less relevant than it used to be, but I believe they are still an easy way to add a meaningful layer of serious communication across a variety of platforms. For all the architectural and social flaws behind the standards, collecting link data is trivial to implement and gives you control of some of the most important pieces of information one can collect: how people are discovering, discussing or re-using your content. One possible advantage is that both the Trackback and Pingback are more-or-less opt-in standards, giving the participants some control over how broadly they want to advertise their discussion. As the public media community keeps pushing user engagement, this is just another tool in the toolbox (and already present in most established content management systems) I've heard a rumor that trackback urls used to be a standard part of the PBS web site infrastructure years ago -- I'd be very interested to know what, if anything, was learned from collecting that data.