As far as I can see, the Collection extension, which provides the Special:Book page, is deployed on nearly all Wikimedia wikis.
Is there data that shows how often do people actually use it?
Amir Elisha Aharoni · אָמִיר אֱלִישָׁע אַהֲרוֹנִיhttp://aharoni.wordpress.com
“We're living in pieces,
I want to live in peace.” – T. Moore