Adding RDF data to web sites has been a problem. In an all XHTML world, it might make sense to embed RDF. In a practical world, I think that it makes the most sense to have RDF files linked via asection link like:
I was playing around with a newer version of the semantic web browsing tool Piggy Bank today, and noticed that Piggy Bank automaticly noticed my foaf.rdf file on my consulting web site. Nice.
Really, adding a few top level RDF files to explain what information is on web sites is not that tough – I need to practice what I preach and add them to my sites KBSportal.com, KBrecipes.com, and KnowledgeBooks.com sites.
Several years ago, I wrote a web spider that would slowly and politely traversed the web looking for RDF files. There were very few that I could find.
When I get some free time, I want to try using search by file type web searches and try RDF data collection again.