Microformat content is only readable and writable as the result of an absolutely tortuous and bizarrely opaque community process. That works if you want to deal with simple and very common things like addresses and events, but doesn’t if you want to add your own custom data.

Despite all the hype of organic evolution that Shirky wrongly says is anathema to the semantic web (and in particular RDF) design, microformats are the technology which actually depends on centralization and limits incremental evolution.

With new technologies like GRDDL, BTW, you can have the best of both worlds: standard microformat-like HTML markup without the tortuous process, but integrated into the robust distributed model of RDF.