Jon Udell touches on the potential for connecting different autonomous tagging systems. We both agree that a Wiki style, inter-system reference language has potential, but Udell adds in the utility of aggregators and meta-search engines.
There's probably enough instantations of these systems, c.f. Connotea, del.icio.us, CiteULike, that a watch/buzz engine specific to them would be useful.
Moment of silence for Gataga... Thank you very much.