My university friend Stéphane Corlosquet has spent the last few months adding a very exciting feature to Drupal for its imminent next release: Drupal 7 will expose your website's structural information as RDFa, by default!
This has huge implications. Drupal being one of the most popular CMS, it handles a significant proportion of the Web's information. So Drupal 7 will effectively make the Semantic Web much bigger. Furthermore, a website's manager will now be able to define the website's ontology based on existing ontologies, which means each Drupal website will now be both a consumer as well as a producer of semantic information.
For website owners, an immediate result is that their website will be better understood by Google. But the Semantic Web is much more than an SEO trick. It is a way to make information more useful, more exact, and to make it understandable by computers.