I’ve posted a preliminary list of the Windows Phone 7 features I’d like to document over the next few months on the SuperSite. These features include hubs, apps, Metro and UI features, settings, and hardware features.
This work will be separate from the book. I’m not sure about crossover per se, but I’d imagine that the web-based stuff will be more of a reference whereas the book is more of a topic-by-topic exploration. There will definitely be information on the site that’s not in the book, if only because it will be a work-in-progress and can incorporate any late-breaking developments and ongoing changes to Windows Phone.
Anyway, if you’re interested, please check it out and let me know whether certain features should be documented sooner, and if there are any missing features you’d like to see added. (Replying in the Comments section may make more sense than email. Your choice, of course.)