IIRC, the WC3 says it’s OK to use RDFa in XHTML 1 or 1.1, although it doesn’t validate (yet).

RDFa’s “about” attribute is very handy. It also allows one to have a single license page that points to mp3s displayed on many other pages / sites.

Commonly, I’d put in my mp3s a URL that points to a singular license page (e.g., example.com/license.html), and then, with RDFa, I can have that page point to all of my mp3 URLs that are spread across many download pages.