I wish had more time and effort to look at personal collection managers, as discussed on Library Stuff. These allow anyone to make a personal catalogue of their book collection. I can think of some (non-librarian) people I know who might find this interesting (if they weren’t too busy writing books) considering they have already attempted to classify all the books they own.
Given the success of Wikipedia with its complex organisation of data and treatment of complicated subjects (e.g.) but with a degree of authority and accuracy that few could have foretold, one wonders whether there can ever be a similar movement for book cataloguing. Given the poor quality of even professional vendor-supplied records, and the difficulties that the intracacies of cataloguing cause for even competent cataloguers, I doubt it, unless a very clever format and framework of rules is devised.