We had a recent "discussion" at work about the BeOS file system, NTFS and the advantages that metadata integration in the operating system brings. Most modern file systems (in the last 10 years) have had some metadata support: HPFS, BFS, Reiser4 and NTFS (in 2000 and above) and the forth-coming WinFS. There's even a proposal to extend OS X's metada support.
Interestingly, "...NTFS5 implements general indexing, which lets NTFS5 store arbitrary data in indexes and sort the data entries by something other than a name. NTFS5 uses general indexing to manage security descriptors, quota information, reparse points, and file object identifiers..."
For examples of the power that BeOS's implementation gave there's the very popular Tales of a BeOS Refugee. BeOS's file system and translators had a direct implication on how applications were developed.
Or is applying metadata to file systems similar to the definition of the Semantic Web: "An attempt to apply the Dewey Decimal system to an orgy."