This is one of those aha! moments. It seems that not only will WordPress pingback a blog entry that you link to within a post, but it’s intelligent enough to find the most recent entry within a category you link to and pingback that entry.
Let me explain. While I was writing up the WordPress Theme Websites and Directories post, I linked back to a category on my design website (powered by WordPress with trackbacks enabled) and I noticed I had received a pingback notification.
It turns out that WordPress found the most recent blog entry published to that category and sent a pingback notification. Of course, this will only work if the blog you’re linking to supports pingback notification and has it enabled.
To learn more about WordPress pingbacks, you can check out the WordPress Trackback and Pingback Tutorial.