I’ve grumped about this a number of times in comments, my own and others, but oddly enough, not in an entry. TrackBack autodiscovery is evil, and will be the death of TrackBack.
When TrackBack was first introduced, it was a way to automatically insert links, with a bit of preview text, in an entry. If you wrote about your favorite catfood, and I wanted to write about how my vet said it was dangerously low in fat, I could leave a comment on your weblog, or, if I thought that my readers would also be interested in what I had to say, I could write my own post about it. Before TrackBack, I could either hope that you would notice referrers from a link in my post, and update your post with a link to mine, or I could leave a comment saying “I wrote about this over here” (something I have never, ever seen done elegantly). With TrackBack, I could either start my post from a bookmarklet, which would discover your TrackBack URL for me, or copy and paste the TrackBack URL myself, send a ping, and have your entry automatically link to mine. Anyone reading your entry would be told that someone else had something more to say about FluffyNumNums, and if “While FluffyNumNums seem like a healthy and tasty cat food, in fact they are dangerous to your cat’s health…” intrigued them, they would have a link to see what I had to say about it.
Then, partly in response to some dislike for the way that TrackBack was implemented, and partly to solve another problem (getting across “I linked to you” without clicking your own links), Pingback was introduced. Pingback has somewhat different semantics (while a TrackBack ping generally has a title, an excerpt, a permalink, and a weblog name, a Pingback ping has a permalink, full stop), and different methods for advertising the URL to ping, but most important for TrackBack, the typical implementation had a very different method for discovering the URLs and sending pings. Rather than relying on the author of a post to decide what entries to ping, since a Pingback ping should be sent for every link to a Pingback-enabled resource (interestingly enough, you can send a Pingback ping to an image, or anything else that has a URL), the sensible way to implement Pingback is just to automatically look for a Pingback server for every link in an entry when the entry is first saved. Pingback solves a problem that needs solving, creating a clean list of referrals from weblog entry permalinks, rather than the usual mix of referrals from various forms of archives and alternate URLs. It just isn’t the same problem as TrackBack, which solves the “everyone is too lazy to go back and update their old entries with links to other entries on the same topic” problem.
Unfortunately, in the ensuing discussion of who had a better architecture and a more transparent system, the fact that TrackBack and Pingback are different things, with different semantics and different goals, got passed over. What makes TrackBack valuable, and makes it worth a reader’s time to click through the TrackBack links in a post that interested them, is the fact that it’s intentional: when you send a TrackBack ping, you should be sending it because you think a reader of that post should read your post.
When Movable Type got TrackBack autodiscovery, sending a ping to any TrackBack URL it could find in anything you link to, TrackBack lost that value. If a reader clicks through some TrackBack links, and finds that the linked entries are interesting, with more to say about the topic, then she’ll be inclined to keep clicking them on other entries. However, if she finds that they are generally from an entry saying “Hey, you should read this“, or a link-dump linking to twenty unrelated other things, or, perhaps worst of all, and done by at least two people who should know better, a linklog that’s nothing but a link back to the entry, then she’ll quickly learn that TrackBack links are there for something else, whether it’s ego, or backscratching, or Google-voting, but are not there to tell her what other entries she should read.
Can TrackBack be saved, while still being more transparent than the original? Sure. All it takes is one step of human intervention before the pings are sent, along with some awareness of what should and shouldn’t be pinged. Either another button alongside Preview and Save, to Discover, or another screen during the entry saving process, listing the autodiscovered URLs along with checkboxes to actually send pings, would do just fine. That, along with enough people deleting pings that don’t actually lead to something more, could possibly return TrackBack pings to being something for readers, rather than something for weblog authors. I doubt it will happen, but it could.