By the formal definition, Microformats designated in the first place for humans and just after to machines. Actually, this is a set of simple informational formats that based over generic and well unified standards. This set of formats comes to simplify common problems into a behavior and common templates (like XHTML, XML etc...).
The main goal of this formats is not to invent a new language or force these kind of changes over the 'world', however it comes to adapt a different way of thinking regarding storing information and publishing it to the world.
I going to apply this set of formats in my new web 2.0 working application. By doing it I can publish to a third level party data from my site easily in unified structure.
So what is the main different from what we have today?
Today we are using XML structure in order to keep data and to publish it or even publishing a specific API that will explain the consumer the way she can retrieve the data. These kinds of solutions spends the developer's time that wants to get the data (she has to learn the API in order to use it); the Microformats comes to save up this time because it's a well know formats.
You can use RSS or some other feeds you'll ask not? In fact yes! BUT, these Microformats has a variety of patterns that help you publish extended unified structure data which supplies you more functionality.
Common standards are: hCalendar which supplies a calendar format in order to publish events, hCard which is a format for personal details card.
One more good advantage is search engines. Step by step, search engines crawlers starts to learn this kind format and knows to index this data in efficient way; this is also improves your site's SEO.
More details regarding it you can read here - http://microformats.org/