I did a little research about Microformats and WordPress that leads to Structured Blogging. But it is not what I expected : they add forms so you can type in, for example the book title, or the author’s name … and they display this information along with your post in a preformated way. Besides, it isn’t exactly Microformats, but microcontent !
What I would like is not a separate form to type metadata, but boutons, like the formatting boutons : Strong, Italic, etc. for metatdata : Title, Author, Keyword … and they would be nothing special to display, the info are in the class attribute (Microformats style).
The usefull part would come from the search engine, wich could then parse the posts and retrieve the metadata, so you could ask for the list of books authors or a movie, given part of the title and the author.