EPUBImporter is Spotlight Importer for EPUB.

I often forget that OS X’s Spotlight can be extended with plugins to index and understand more types of data across more files. This EPUBImporter project lets you build a plugin to handle

eBook files, and maps the metadata and contents accordingly:

This means that

books living on indexed volumes can be found via Spotlight, which will be very handy when OS X Mavericks is released and iBooks is de-coupled from iTunes letting you read your books and access highlights, notes, and annotations anywhere.

EPUB Importer for Spotlight