Very quickly: microformats are an XHTML specification which supports the encoding of contact data (hCards), dates and events (hCalendars), reviews (hReviews), and other formats in regular XHTML code, thus enabling machines to successfully parse data out of the same URIs that people can read themselves. This saves developer time and makes the content more semantic and search-engine friendly. Read John Allsop's blog Microformatique for a more in-depth yet approachable explanation.
You can download the CFCs here. Please use them, modify them, and give me feedback! I hope that lots of people find them helpful.
Just added: I've created a listing for this project on RIAForge at microformats.riaforge.org