Myself, and Leigh Dodds of Ingenta, recently spoke at the Oxford SWIG. We were both talking about SPARQL, the standard query language and protocol for the Semantic Web.
Eamonn Neylon, who organized the session, has written up a summary of the talks. I was talking about DBPedia and how to write SPARQL extension functions; Leigh was talking about his SPARQL tool Twinkle, and about the different SPARQL query forms (SELECT, DESCRIBE, CONSTRUCT, and ASK) and what they are useful for.