On our site, with mainly tekst (we don't allow attachments), we generate around 70 gb monthly.

awstats reports around 50,000 unique visitors, 3880265 pages, and 27067916 hits.

This runs comfortably on a shared hosting environment.

As for forumstats:
28 Forums
13697 Topics
487359 Posts

And most of this stuff is from the last year only, older then that goes into our archives.

[Linked Image from siemons.org]