I just read an article http://www.kuro5hin.org/story/2003/8/9/172159/7912 about giving
file systems more of a database's capabilities.

I've already been using reiser4 on my laptop for a few months but don't see how a
user can associate any custom meta data with a file.

I guess this is because there would have to be a universal standard to access those meta fields for a file before they you can associate arbitrary meta data, because otherwise a song with it's artist and release year stored as meta data won't be able to transfer to a non database file system. If that's the case, then I don't know how long it will take for database file systems to become the norm since Microsoft will always be dragging everyone else's feet.

Also does this mean that the C library will get new stdio functions for handling meta data?

Filesystems with seperate metadata have been used in other operating systems (such as Mac OS, if I recall correctly) for years now.

Personally, I'd like to see a non-hierarchical filesystem (using a full SQL RDBMS with inherited tables for various types of file, with relationships linking them) but that's probably just me.