There is a quite a bit of semantic-web data available on the web. But you won’t notice it unless you keep an eye out for it. The following firefox extensions can give you semantic information about pages you are browsing.
Semantic Radar [1]: shows an icon in your status bar if a website has exposed rdf data such as FOAF [2] or SIOC [3]. You can then click it to view the SIOC information or the FOAF profile.
FOAFfox [4]: tells you if a site has a FOAF profile. This functionality is also in Semantic Radar so there is no need to install both.
Operator [5]: tells you if there are microformats [6] available on a page. Also allows you to combine data from different sites that are using microformats.
Tails [7]: allows you to view microformats embedded in a page.
Piggy Bank [8]: allows you to browse, aggregate and combine RDF [9] data in your browser. Also allows you to scrape data into RDF from pages that don’t contain RDF.