[johnhiler]

_ck_ prepared a list of the top 100 sites here:

https://bbpress.org/forums/topic/bbpress-top-100-april-2009-update

The largest site has 1.6mm posts; the site with the most users is wordpress.org, which has 7.5 million users.

http://bbshowcase.org/forums/view/top100

Hope that helps!