WordPress is a great system for personal semantic publishing and is more than adequate for the vast the majority of websites. No other CMS can match it for simplicity, ease of use, breadth of plugins, and an active developer community.
However due to its blogging background it has one very substantial weakness. Namely there is no way of easily relating one post to another and detailing its realationship. Of course taxonomies can be used to group posts and provide some form of relationship. However this is not an elegant solution.
This issue has been raised before by the WordPress development team here. Some use cases are outlined, however, I think the discussion (which is now closed) misses the elephant in the room, semantics. WordPress claims to be a semantic personal publishing platform but until it has the ability to seamlessly and elegantly relate one post to another it will be nothing more than a publishing platform, and until it then exposes those relationships in an unabiguous machine (and human) readable format it will never be truly part of the semantic web.
Frustrated at this weakness I am releasing a series of plugins that will truly RDF enable WordPress.
The first is LH RDF. LH-RDF is a wordpress plugin that automatically creates a SIOC compliant RDF feed of wordpress posts, categories, tags, and author ojects. It comes with embedded content negotiation thus properly exposing WordPress’s existing linked data to the semantic web.