I just read this article on where semweb technology really works well. The context of the article is searching and points out how semantic search excels at essentially performing complex relational queries over the web.

Hopefully, it is clear from some recent discussions of tools like eXist and XML focused data stores that there is a market for generic XML document stores. Conceptually, I think this kind of technology is similar to CouchDB with the difference being there is a wealth of XML libraries to help more complex processing, where CouchDB might be more limited to specific usage where JSON excels. I’m not suggesting either technique is better, but rather the idea of a document store that can be queried in more typical SQL-like contexts seems to be gaining popularity. Taken within the context of RESTful services, I think it is a killer combination.