RDF is worth learning for a different reason — the profound enlightenment experience you will have when you finally get it. That experience will make you a better format and data API designer for the rest of your days, even if you never actually use RDF itself a lot. (You can get some beginning experience with RDF fairly easily by writing and modifying simple files like FOAF and DOAP for social networks and software projects, or RDFa extensions for XHTML.)
2008-10-15: The Semantic Web Deployment Working Group and the XHTML2 Working Group published the W3C Recommendation RDFa in XHTML: Syntax and Processing. This specification allows publishers to express structured data on the Web within XHTML. This allows tools to read it, enabling a new world of user functionality, allowing users to transfer structured data between applications and web sites, and allowing browsing applications to improve the user experience. For those looking for an introduction to the use of RDFa and some real-world examples, please consult the updated RDFa Primer. Learn more about the Semantic Web Activity and the HTML Activity.