I love the way learning is never a straight line...
Semantic clustering, which I included in a list yesterday is not the same as the other items in the list. Semantic clustering turns out to mean clustering based on the items shared/downloaded on a p2p network... which makes since when you consider the name.
Describing an intimately designed system containing subtle but elegant features is difficult. I'm finding it hard to lay out the details in simple but meaningful ways while managing to convey the importance of each piece. Each piece both contributes to and relies upon the success of several other pieces, making them terribly subtle on their own... it is the synergy that holds the work together, but simply describing synergy is daunting.

Scratch semantic clustering from the list...