By now everyone has heard that WinFS (the new SQL-based, meta-data driven file system) won't be shipping with Longhorn. It's not really surprising. Not only is it a fairly challenging technology, but the surrounding behavioral issues are, IMHO, an even bigger deal, and will take a good long while to resolve.
The reason meta-data based solutions haven't dominated the world have nothing to do with technology. RDF works just fine. So do XSD and Web Services. So does SQL server, so I'm convinced that the technical hurdles to achieving WinFS are solvable. The trouble is getting people to use it. People just don't get it. Nobody uses RDF, in part because it's way to complicated, but also because most people just don't get meta-data. It's hard enough to get people to use proper keywords on their HTML pages.
Similarly, the reason that Web Services have yet to revolutionize the world of B2B eCommerce have nothing to do with technology. The parts of the technical picture that aren't solved by SOAP/WSDL are quickly being addressed by WS-*. The real issue is schemas. The barrier to real B2B isn't security, or trust, or routing/addressing, or federation even. It's the fact that no two companies in the entire world can agree on what a PO looks like. The barriers are institutional, not technical.
The same thing applies to WinFS. Even if the technical side can be made to work reliably (of which I have no doubt given enough time), it's the institutional issues that are hard. What do you call the tags that get applied to your file system? If any applications are going to take real advantage of them, they have to be agreed upon in common. Anyone remember BizTalk.org? It's not easy to reach consensus on what seems like a simple problem. What do you call the meta-tags that are applied to your data? It's great that you can arbitrarily add new tags through the explorer, but if no application besides explorer supports them, is it anything more than a great new way to do sorts?
I think in the long run it's that problem that has delayed the release of WinFS. There has to be a plan in place for handling the institutional issues in place first, or MS will end up with another great piece of technology that no one knows what to do with.