no one uses them, if they did, search engines would ignore them

From a brief read, microformat's appears to be yet another attempt at serialising data in a human readable form that is still easily parsed by a machine. Granted it's a bit unusual in that it doesn't define a format, but rather re-uses existing formats like HTML, JSON, and XML. The core of it appears to be defining naming conventions, and how they should be applied to those formats.

If I was to evaluate it, it would be on whether the naming convention is worth using as opposed to just rolling my own. That could depend on all sorts of things I guess - like availability of compiling and parsing libraries, how many people are likely to want to parse the data I published, how frequently it changes, and who would be using. The one thing it is unlikely to depend on is what a search engine thought of the resulting HTML. And the one thing it absolutely would not depend on is whether it might be adopted by soe practitioners.