Questions on personal categorisation

Had an interesting discussion with Anjo and Rogier on how and why people categorise things (documents, bookmarks, blogposts)... Thinking of all kinds of things that I'd like to know about my own categorisation:

• Why I categorise things the way I do? What are the criteria?
  
• When I categorise things for further retrieval, how often I actually go and retrieve them? Does categorisation helps in it?
  
• How categories evolve over time? In relation to: changes in thinking, changes in tasks, changes in tools I use?
  
  
  
  • e.g. did categorisation in my weblog changed since I started to use del.icio.us
  
  
• How categorisations in different spaces (e.g. file folders, email folders/tags, paper files, weblog topics)overlap? What explains overlaps? How you could connect them? Is there a need to connect them?

Just a brain dump...

See also: LiveTopics wishlist or topic-based blogging support on how I categorise things in my weblog and what features I miss.