"In practice, if you forget about system files and such, I'd estimate 9 out of 10 people have all their documents in a single flat folder, which they only access through their word processor or whatever they use to open them."

9 out of 10 home / casual users: perhaps true. Among teachers using the 70 staff computers in this large open plan office, there is an amazing variety of carefully organised folder structures and layouts that typically, for each teacher, organise 8 to 10 courses each consisting of two sessions a week for 36 weeks. With overlap. And shared folders with colleagues.

If we used Mac OS X instead of Windows, it it really is the case that you can only have one level of folder, then my colleagues would have to recreate their heirarchies using file naming conventions. Messy, and hard to manipulate.

A database approach might yield an actual benefit: I'm assuming that would look a bit like Outlook's message view where clicking on the from, received, subject fields allows an instant reordering of the material. But tree like re-orderings would be needed to allow my colleagues to continue to organise their content as they do now.

Part of me likes the Jef Raskin approach, the content is the file name and you use incremental search to find a particular part of your work. It is hard to see how that works for media files.

I have no issues with changing how we organise material, but there does seem to be a shift in assumptions on how people will use their computers towards the superficial media stoage and comsumption sort of model. That won't fit everyone at all.