This past summer, Hugo Dworak worked with us (thanks to Google Summer of Code) on a new validator. This work was greatly overdue, and we are very pleased that Google could fund Hugo to work on it. Our previous validator had not been updated to reflect our new metadata standards, so we disabled it some time ago to avoid creating further confusion. The textbook on CC metadata is the "Creative Commons Rights Expression Language", or ccREL, which specifies the use of RDFa on the web. (If this sounds like keyword soup, rest assured that the License Engine generates HTML that you can copy and paste; that HTML is fully compliant with ccREL.) We hoped Hugo's work on a new validator would let us offer a validator to the Creative Commons community so that publishers can test their web pages to make sure they encode the information they intended.
Hugo's work was a success; he announced in August 2008 a test version of the validator. He built on top of the work of others: the new validator uses the Pylons web framework, html5lib for HTML parsing and tokenizing, and RDFlib for working with RDF. He shared his source code under the recent free software license built for network services, AGPLv3.
So I am happy to announce that the test period is complete, and we are now running the new code at http://validator.creativecommons.org/. Our thanks go out to Hugo, and we look forward to the new validator gaining some use as well as hearing your feedback. If you want to contribute to the validator's development or check it out for any reason, take a look at the documentation on the CC wiki.