Microformats are a cool way of making web content machine-readable. Since the formats rely on classes, they also ensure the content has all the hooks needed for good CSS design.
Microformats can be understood by aggregators like edgeio and consumed with software like Firefox 3 and the Tails extension for Firefox 2. We have been introducing Microformats to all sites and applications we've produced since mid-2005.
However, I've noticed lots of customers and even web professionals are not really aware of Microformats yet. For them, here is a great introduction by Alex Faaborg: