Number of downloads of monster books.

3723 - Dor Un Avathar
2270 - By Night They Dance
1824 - Nautical Nights
1696 - Celestial Codex: The Eternal War on Amtgardia
1620 - Welcome to the Jungle

This isn't including any copies that are hosted on other sites, like www.amtgardinc.com, or downloads through direct links.