For people interested in this subject, you might want to check out the DBPedia project: http://dbpedia.org/About. They have been extracting structured data from Wikipedia for quite some time already and allow you to query their database with SPARQL.

From their site: The DBpedia knowledge base currently describes more than 3.64 million things, out of which 1.83 million are classified in a consistent Ontology, including 416,000 persons, 526,000 places, 106,000 music albums, 60,000 films, 17,500 video games, 169,000 organisations, 183,000 species and 5,400 diseases.