Arnaud Leene talks about "Wild Microcontent" (see also: Web 2.0 Checklist, and a note about his old and new review blogs).
I remember chatting about this with Marc Canter and David Galbraith in San Francisco two years ago. The contept is that microcontent isn't limited to blog posts, events, reviews, audio, video, and so on, but that there's an infinite variety of stuff that people want to present in a structured way. So why shouldn't people make up their own microcontent types?
Update: Joe Reger's datablogging (top-level explanation) idea is very similar. He's actually implemented it - you can see the new fields in his RSS feed. Here's the namespace and the XSD for the XML. <field> with children <fieldname>, <fieldid> and <data>, with <data> having children <name> and <value>. Verbose! Here's an explanation in English.