Semantic Wikipedia Query is based on dbpedia.org, which is a community effort to extract structured information from Wikipedia (~ 91. mio. triples) and to make this information available on the Web. It allows you to ask sophisticated queries against Wikipedia and to link other datasets on the Web to Wikipedia data.
This project shows why the semantic web won´t fail: In contrast to simple queries against full-text indices, semantic queries (similar like SQL-based database-queries) allow queries like “show me all projects we´ve done in Russia the last 10 years”. Semantic Queries in the Semantic Web can be realised deploying SPARQL-endpoints and are one of main advantages semantic wikis have compared to classic wikis.
Another great benefit when all the information on the web is “tripled down” comes up, when meshups (with geo-information or foaf-profiles) are realised.
Also try out dbpedia search!