US Government Website uses XForms, XHTML, and RDFa
Quoting this post:
"This followed another talk there by George Thomas, from the U.S. government website recovery.gov, on how the site will put information on the government's economic stimulus spending into the semantic web and the Linked Open Data world via Atom, XHTML, and RDFa. (Very cool.)"The slides add XForms to this mix.
Update: shortly after this, the man who was responsible for the site, Vivek Kundra, got appointed as the first-ever Federal CIO in the USA.