structuring subject data

has anyone successfully tackled the problem of categorising their subject, I'm trying to get a site together holding a hierarchy of subjects, which can then be linked to by end-users (the public at large) through their personal spaces. The idea is then to be able to link end-users together based on their common labels, which would also link to the editorial content.

at the moment i'm creating the hierarchy of subjects by simply building page trees, and then putting relevant labels on the children. but when it comes to having the end-users label accurately from their personal spaces, they are pretty much going to be on their own.

I realise we can go the folksonomy route, but i was wondering whether anyone had gone for a more structured method.