I need this for storage and retrieval of information across almost every aspect and area of my life.
I've thought about addressing this using one layer of meta-classification: a way to classify the classification systems so I can find them/remember what they're for. To avoid absurdity it would be best if this idea could be collapsed back into a single classification ("filing") system as an added feature. Perhaps an interface to the classification system that exposes such metadata about each label or category as one is applying it.
PersonalBrain from thebrain.com does this pretty well, but it's still hard to publish from, and somewhat hard to integrate with other systems.
Any ideas, readers? What kind of filing systems do you use? How do you remember things? How do you remember why you remembered those things?