Erik Benson, in summarizing his view of ETech and SXS2 2005, hits on a point which gets continually washed out by the taxonomy/folksonomy arguments: people tag things for many different reasons, concluding that people aren't being rational in their tagging. The big hope is that a pile of autonomous labels will reveal patterns of classification.
Hidden in there are patterns of communication, coordination, and collective activity. C. f. The Gates Memory Project, Squared Circle, and Day In The Life Of....
Tags are used as much for signaling others as they are a remembrance device.
Oh, and being in Chicago, I have to say "less is more".