Wikibooks contains a number of annotated texts and reading guides, but none of them are as famous as the Muggle's Guide to Harry Potter. The Muggle's Guide contains information on all the books and other media associated with the Harry Potter series, and is already bracing for the influx of new readers and contributors with the release of the newest book in the series: Harry Potter and the Deathly Hallows. This book has already attracted over 500 edits in the past week (which is a large amount for any single book), and that number is expected to rise dramatically.
All the site admins and RC patrollers have been asked to keep a special eye out for this book, both to revert the inevitable vandalism, but also to warmly welcome all new potential contributors. Already some of the most active contributors to that book are taking a brief wikibreak to actually read the book, during which time they can all expect to be less active then normal.