I haven't looked at Spotlight at all, but from your description it sounds like RMS on the VAX from 20 years ago. Every file in RMS has metadata - a couple standard blocks for OS stuff and any number of extended blocks for arbitrary other metadata.

Windows unfortunately followed the lame-ass Unix file system model rather than something more robust like RMS and I've been missing those features for a very long time now. It is odd really, since the Windows kernel was created by the same guys that created OpenVMS, so you'd think they would have brought the good file system along too...

In any case, even RMS couldn't do the things Microsoft is hoping to do with WinFS. In particular the virtual views, which rely on high-speed indexing of the metadata, which does imply that the metadata can be stored in some indexed form rather than attached to each file. That really leans toward (though doesn't require) a database engine.

I think it'll be a good demonstration of "How not to overarchitect and turn a greyhound into a big fat pig"

In response to Rockford's comment, the metadata is actually located in a central store rather than with the file. There is a separate context index to allow for faster searches and is updated when the file is created, copied, updated or deleted. It is actually pretty sweet technology.