On the topic of mining Wikipedia, DBpedia (http://dbpedia.org) is a fantastic source for structured Wikipedia content. Extracting data is pretty easy with SPARQL.
Freebase (http://freebase.com) isn't bad, either.
Freebase (http://freebase.com) isn't bad, either.
"DBpedia is derived from Wikipedia and is distributed under the same licensing terms as Wikipedia itself" http://wiki.dbpedia.org/Datasets#h18-19
Please correct me if I'm mistaken!