Besides consuming Microformats - it's useful to know how to produce them. Assaf Arkin has extracted a Microformat Helper from his scrAPI plugin. It supports hAtom, basic hCard, and the datetime design pattern currently - and should be easy to add some more microformats. Check out his Microformat Helper Cheatsheet if you're addicted to that sort of thing.

Out of the Ruby realm, BlogHelper has a good set of tools and howtos for Using Microformats in WordPress.