Someone pointed out this clustering application for del.icio.us. Its just for clustering your own data though, so its not leveraging the group mind. Still it was interesting to see the clusters formed by my tags. Some of the clusters were: clusteranalysis(!); visualization; mobile research; market research; flash; ajax; cardsorting; design.
Expectedly, they are using k-means clustering algorithm. I played around with the number of clusters and the cohesiveness of the clusters does change as the number of clusters goes up.
I looked at the del.icio.us mindmap maker as well. Was not able to view my own map (browser had some problems loading Java files. when are they going to be able to create a smooth install experience for java!).
All these clustering efforts lead to one conclusion. I am repeating myself when I say that tags call out for clustering. Watch out for more types of clustering efforts. It would be ironic if someone someone tried hierarchical clustering, and created a personal taxonomy – which people like Clay Shirky have railed against.