Seb Paquet captures a potential emerging trend: commentlogging. If I get the gist, folks are using del.icio.us to record the places they leave comments across the blogosphere, squirreling them away for later examination. This also helps in monitoring the overall discussion.
By itself, this is an interesting usage of del.icio.us, but combined with Robin Millettee's durl service for monitoring del.icio.us URLs, or conceivably PubSub, some second order effects could kick in. I've been a big whiner about the impoverished nature of blog conversation versus classic USENET, but this seems to hint at further steps down the slippery slope of centralizing conversation. I'm pondering whether there's any significant improvement or extension but haven't seen any glaring wins. Still this might be an emergening phenomenon to keep an eye on.
Only problem is, making del.icio.us the sole conversation server, polled to boot, doesn't seem like a good idea to me.