I'm convinced that the marriage of web content with semantic web meta-data is the future of the Internet. (This isn't a big leap and lord knows I'm late in saying this.) The main reason why people like me are so late to jumping on board this slow moving freight train is that while the theory is all there, and is very solid, the tools just haven't been coming. There's little obvious incentives for the groups that are the builders of the web to make their products semantic web friendly, and even when they do their only interested in doing so to lock you into their product. Linking things together, even though it is the entire purpose of the semantic web, is like pulling teeth. The reason for this is simple: there is an almost complete disconnect between traditional databases, which are the life blood of the web, XML, and semantic databases. The engines are different. Their query languages are different, and their interfaces are completely different. While there has been a lot of effort to create a bridge between relational databases and XML, there has been little to add a bridge connecting it to RDF semantic data.
Most of the initiatives have are hard time at acceptance because they make the same mistake that most failed projects make: they completely reinvent things instead of trying to seamlessly integrate with what already is. Very few people are going to abandon their desktop for a "semantic" desktop. They've invested too much intellectual and emotional capitol in their existing interfaces. Forcing them to abandon everything that is in addition to learning a whole new way of envisioning data and its relationships is completely unrealistic.
Semantic Web data is designed to make it easier for machines to process what's on the web. It is a construct that needs to be relegated primarily to the machines in order to be effective. When the users don't even think about it because they are so lost in the ideas, THAT'S when it can be considered successful. (This is true of all of what I call the invisible arts: typography, movie soundtracks, etc)
There are two products that I know of that have successfully bridged this gap: Fedora-Commons and OpenLink Virtuoso. Each has their strength and their weaknesses.
I'll provide a comparison between them soon.