I have recently discovered the joy of social bookmarking -- check out my tags at http://del.icio.us/dglane001
I think the non-heirarchical organization enabled by tagging is very liberating from my previous, hierarchical bookmark scheme (which was based on Mozilla Favorites organizer).
I'm also intrigued by the consensus use of tags, in the absence of any specific priming as to what they "should" mean. Of course some tags clearly have multiple senses, but its interesting that a lot of different people would converge on associations for particular tags. I guess that's analogous to how language may have evolved.