I'm a big fan of trackbacks, at least in theory. A trackback, for those who may not be familiar with them, is a widget which automatically lets one reference a blog or webpage and automatically let the owner of the other website know that you have referenced their page.
Trackbacks, as with links, help readers find blogs and websites of like mind and interests. Trackbacks help authors know which of their posts have generated the most interest.
My one fear is that trackbacks will soon be under attack from spamsters and that this wonderful widget will be rendered useless.