Another idea, probably not new, but may also lead to problems with current clients:

I'm rather unsatisfied with the fact that most people use the file name to put in many keywords to describe them and to enhance the probability of being found. But there are file systems which cannot deal with such long file names (e.g. Mac-HFS, or CD-Jolliet). Just read the file names of some XXX movies and you know what I mean...

It would help in such cases to allow some additional description to be attached to a file; of course it won't be easy to keep them together without limiting the access to the main file. Have there already been any ideas about that topic?