Microformats in general, but espcially xfm, seems to be a perfect basis for tools that track the spread of news and memes in personal network, like the blogosphere. A simple blogroll is already a good hint how the neighbourhood of a blog looks like. XFM would provide more detailed info about the nature of a relation:
XFN outlines the relationships between individuals by defining a small set of values that describe personal relationships. In HTML and XHTML documents, these are given as values for the rel attribute on a hyperlink. XFN allows authors to indicate which of the weblogs they read belong to friends, whom they’ve physically met, and other personal relationships. Using XFN values, which can be listed in any order, people can humanize their blogrolls and links pages, both of which have become a common feature of weblogs. (Source: xfm)
