I've used Haloscan's trackback service since I started this blog (it shows up via the little "Trackback" link underneath each post). However, now that I've upgraded to the new blogger, I've fiddled with my template to enable backlinks (the "links to this post" link that is now showing up below the posts).
Backlinks automatically display links from other posts (on my own blog or on other blogs) that refer back to the original post. This is a pretty cool feature (I especially like that it shows when I refer back to a post), and it functionally eliminates the need to use Haloscan's trackback service. I'm going to use both for a short while, but assuming backlinks continue to work well, I'll probably delete Haloscan's trackback links at some point.