not sure about microformats...
finished the Microformats book this evening and i'm not yet sold on the idea. i admit i like the idea of standardizing X/HTML markup. that's nice. but i'm not sure i am ken on the notion of making X/HTML pages more friendly to machines via microformats. i think RDFa or eRDF are much better suited for making X/HTML machine-readable.
finally, if you really want to do all that, it seems that it's better to simply implement RDF and let RDF tools handle the work directly. i'm not feeling the idea of supporting multiple mime-types with a single document at all.
finally, i think the "element" microformats ("rel", "rev", etc.) *do* make good sense. they are a simple way to improve the value of your X/HTML markup without doing any other major "processing."