an update of the use case document

Hi all,

I've updated (and will continue to update today) the use case document:
http://www.w3.org/2006/07/SWD/RDFa/scenarios/

If you have a chance, take a look at it quickly and send me your
thoughts. I'm just applying the WG's requested changes about not having
any RDFa markup in the doc, stating the principles more clearly, etc...

I'm still working on the section that was requested about "difference
with microformats" and seeing how to integrate TimBL's additional use
case of RDF lists.

-Ben