collaborative bookmarking / categorization as annotation?

Hello

Is it a good idea to strore categorization of a document as annotation?

An annotation to associate a page to a dmoz-category could look 
something like this:

<r:RDF xmlns:r="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
        xmlns:a="http://www.w3.org/2000/10/annotation-ns#">
  <r:Description>
   <r:type 
r:resource="http://www.w3.org/2000/10/annotation-ns#Annotation"/>
   <r:type 
r:resource="http://www.w3.org/2002/XX/annotationType#Categorization"/>
   <a:annotates r:resource="http://serv1.example.com/some/page.html"/>
   <a:body r:resource="http://dmoz.org/rdf/#top/arts"/>
  </r:Description>
</r:RDF>

If the annotea protocol would allow to retrieve a document annotated 
with a specific annotation body, applications for sharing bookmarks 
could be realized.

Are there other protocols designed or usable for communication with a 
bookmarking server? Is there a RDF/Schema for web-page categorization 
(I know only about the one used by dmoz)?

Thanks.

Reto