I like this post from Tantek. In his XML Design Notes, Tantek mentions two simple thumb rules:
In order to help people reuse (assume that they have no motives for reinventing).
1. We need to make the information and usage patterns easy to find
2. We need to make small variations/extensions easy to do (for example, it should be easy for me to add some new element/attribute to a specific microformat for corporate use)
3. We need to make it easy for people to write and share reusable XML elements. I think microformats are a good way to achieve this, though I have not written one to see whether they meet the criteria.
Microformats.org is doing a good job of the educating users on simple reuse and development of structured content.The geek in me tells me to use RDF since it is so much more powerful and cool, and the pragmatist in me says that I can start simple with something like Microformats and see how far I can go.