Technology First, People Second
David's analysis is spot on, but the comment that popped out at me was the following:
Ironically, technology is the starting point for Last.fm’s relatively social approach (i.e. the Audioscrobbler application) while people are the starting point for Pandora’s largely technological approach (i.e. musicians’ and others’ evaluations of music on a specific set of attributes).
I have always thought that the most vibrant web services use a combination of technology and people to produce the value.
But I have never thought specifically about the order in which the two need to be brought to bear on the issue at hand.
My initial reaction to David's post was that technology has to come first and people have to come second. I think that's the most scaleable and most natural way to architect a web service. But maybe that's not right.