[RDF] is an extremely flexible language, but unfortunately it's too young for best practises to have been established (the [W3C] has reacted by forming a Best Practises working group). Many of the common schemas are still in a state of flux, and noone's quite sure what predicates to use for things or how to use various predicates. Another problem at the moment is that there is no obvious way to embed [RDF] data in a web page, just to link to it as an alternate or related document. 

  

 People complain that [RDF]/[FOAF] violate privacy, but the intent is really just to have a mechanism to talk about a person in machine readable fashion. For instance, it's common to include contact details about the author when publishing a document, stating their name, their email address and perhaps home page. Providing this information as [RDF]/[FOAF] enables computer programs to process this information directly. This way you could search documents by author or send them a mail without having to manually cut and paste the information. DashBoard is an example implementation of this concept. 

  

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 [1] There are 9 incompatible schemas/DTD that claim to be "RSS", half of which aren't even remotely [RDF]-based.