Trackbacks don’t quite work the way I thought they did. I assumed it was some automatic thing, where, as long as they were enabled, linking to another blog entry automatically created a trackback. In reality, you have to manually send a ping each time you want a trackback link to appear on a blog you link to.
HaloScan now provides my trackbacks and comments. It seemed at first like my native Blogger comments (all 3) were lost, but they are still there with the permanent links. HaloScan seems nice and non-invasive (and the link I added on the side was voluntary, though requested). When you try to add a comment, there is a pop-up that has a few ads, which must be how they provide the service for free (along with donations), but the ads are at the bottom, and don’t get in the way of anything.