Similar to outside efforts like Microformats, HTML5’s microdata offers a way of extend HTML by adding custom vocabularies to your pages.
Using microdata, you can create your own custom name/value pairs to define a vocabulary that describes a business listing.
Microdata is useful today, but what about Microformats or more complex tools like RDFa? The answer is that all three will work (and Google, in most cases, understands all of them).
In the end, the differences between the three are primarily in the syntax, and each has its advantages and disadvantages. But given that the Microdata specification will very likely become an official recommended web standard as part of HTML5, it seems the most future-proof of the three options.
I have been an advocate for microformats for a long time, it’s interesting to see a variation on the same theme baked in HTML5.
A Frog in the Valley 