Tom Coates does some interesting interface thinking in regards to tagging and folksonomies. Most of the thought process is in how to incorporate tagged bookmarks into Safari, some of which has already been done for Firefor. Coates mainly approaches the topic from the angle of Flickr's tags but of course del.icio.us makes an appearance.
The comments are also worth reading, although of course a librarian, archdata, shows up and doesn't quite get the spirit of del.icio.us. As far as I read the zen of del.icio.us, tagging is purely personal, but just happens to be in public. The goal is not to come up with some beautiful, efficient taxonomy that everyone can share. That's too much work to build and to use. del.icio.us is designed to be as simple as possible, to get as many people to use it as often as possible. Splendid chaos ensues.
One sort of neat idea Coates had was the construction of ad hoc social connections being created through local aggregation of individual folksonomies. Imagine if Rendezvous was used to publish people's del.icio.us URLs. On the fly interesting intersections of tags and tagged urls could be built and examined. Don't really know where to go other than that the notion of on the fly, ephemeral, social media spaces seems like an interesting are of exploration.