When I first started blogging, I was always confused by the word "trackback" that I saw appear everywhere.
I still think it's mis-titled.... it should be called something like "Tell Me You Linked To Me!"
Anyhow, for some reason, Blogspot / Blogger don't support them.
But now, Haloscan are offering a service that lets you add support for yourself. Neat!
I think Trackbacks are probably an interim solution until the search engines are quick enough and thorough enough to track the web of links more comprehensively but that's no reason not to use them in the interim.