At some point, I'll get around to starting some pages for discussing an API microformat and a logging microformat.
Sitemaps and WSDL may provide the foundation for an API microformat. I know that microformats shouldn't be invented where there isn't already something useful out in the wild that just needs a way to exist in xHTML. WSDL and sitemaps are examples of useful data that could be more useful if placed into a human and machine readable structure. Somewhat like Doxygen, this sort of microformat could be used with a site's REST API documentation. Just as WSDL is useful for SOA application development, this microformat would be useful for applications using REST.
In the meantime, read my blog at Chaotic Clamoring. I talk about microformats every now and again.