I missed this nice post from Zeldman at the Daily Report, in which he points out the need for imposed structure alongside a tag soup:
Jeffrey Zeldman Presents The Daily Report: We who make websites must strike a fine balance between guiding our users and allowing them to lead us. We listen but we also synthesize and invent. We conduct user research but we interpret the results. We ask what users want but we decide what they are really telling us – and we, not they, determine how best to fulfill the needs they didn’t necessarily realize they were articulating.