RDF data in Lucene?

Does anyone have experience adding RDF data to Lucene (or other search engine) index? And now I'm not talking about indexing RDF data (string literals, labels, instance names, etc.) but adding RDF metadata to documents in full text index.

A good use case is when indexing RDFa+HTML documents. How to store the RDFa information next to the full text index? Is there any best practice regarding this (like regarding the index profile, etc.)

Other interesting question is how to query such a structure.

Rob, are you aware of SIREn? I think that should do the trick ...

I can't see the difference between indexing RDF documents and RDFa documents. Sindice has been crawling and indexing documents with RDFa. Maybe this will inspire you to some extent.