Making heavy use of custom post types to turn WordPress into a web application, PressBooks allows you to enter your book content into WordPress and export it in a variety of formats. It also allows you to invite other users to contribute to your book via the WordPress users system.
Your book, which gets its own public or private subdomain on PressBooks.com, can have multiple authors listed along with standard meta data (title, subtitle, publisher, publication date, etc). Front cover uploading is supported, but uploading a full cover (or back cover) seems to be missing for now.
Entering your book’s chapters is like adding posts to a blog using the standard WordPress content editor (including the distraction free mode if you choose to write your book vs. copying it in). Chapters can be dragged and dropped to re-order and organize them into parts. Extensive front matter support is present, but end matter support seems to be missing from this initial release (e.g. an index, colophon, epilogue, etc).
When you’re done entering your book, you can export it to ePub (in three styles), PDF (3 styles), and two XML formats: InCopy markup language (ICML) for import into Adobe InDesign and Wikibook XML. Hopefully PressBooks plans on adding additional output styles (and custom or community contributed styles) to allow for more variation in formatting.
Your book also gets a website allowing visitors to read you book online if allow it.
PressBooks is targeted at publishers looking to streamline how they receive content from authors and authors looking to self publish their books without having to pay for typesetting. I’d say it looks like a solid service that will only get better with time.
Would you use PressBooks to typeset your next book (or e-book), or would you rather leave it in the hands of a professional?