From Brian Suda’s “XFN encoding, extraction, and visualizations“:

In this article I will take a good look at XFN – the microformat for describing relationships between people. I will look briefly at what it is and the basic markup needed to add the information to your sites, before then going into depth, looking at the benefits you can get from that data by extracting it and using it in different ways. Extracting the data is easier than you think – there is probably a library for your favorite language already! If not, there are also some web services that could do the job that I’ll show you below.

Via a Microformat tweet.