Google has been using microdata for quite a while now and adding it to your website can help with clickthrough rates from search engine results.
The most obvious is Google’s own authorship markup (not strictly microdata per se) where linking to your Google+ profile adds your profile image to pages in search results, but there are many other tags which can be added to display extra information next to your page title and description.
In this article I am going to look at adding microdata for article publishing times, images and authors to Joomla 3.