http://twitter.com/microformats
Such as:
hCalendar - see upgrade Date cardtype
http://microformats.org/wiki/rel-tag - for blogging, etc.
Firefox add-on for reading/using them: https://addons.mozilla.org/en-US/firefox/addon/4106
More recently: http://schema.org/
Seems more like a shiny object than a significant feature. A new name for common sense practices.
A general means of adding enclosing markup (as a view?) to a given set, which would handle many use cases involving microformats, would be a pretty significant feature imho.
Implement microformats+discussed in support tickets
Implement microformats+relevant user stories