TPTB:
I am considering using this BB software on my own humble site. However, disk space is an issue. How much space does each post occupy? Perhaps it would be easier to state it in units of thread; how many kb is an average thread of, say, 30 posts? Thanks!
Depends on whether Duck Duck Goose is in the thread! 
Well, Mr Astronomer, let me give you some statistics from the UnaBoard (which is also a vBulletin site).
As of right now, I have 8018 posts on my Board, within 568 threads. That’s an average of 14.1 posts/thread.
The total size of the database is 12,463,000 bytes (11.8 MB), of which about 3.9 MB are posts and post indexes, and 4.3 MB is the Search index. The size of the software you have to install to make this run is:
Apache 1.3.19: 4.0 MB
PHP: 1.0 MB
MySQL: 21.0 MB
vBulletin: 3.0 MB (includes tons of avatar graphics)
So, overall, you can get 8000+ posts on your site for about a total of 41 MB, including all the software.
Sorry…forgot to mention that is an average of 1.5 kb per post overall, including the Search indexes.
Yeah, that Mad Hatter thread must be several times the size of a post count party.
The webhost I use already has Apache, of course, PHP and MySQL. So I guess I don’t need all that much. I wouldn’t include avatars (I pay for bandwidth) so this might just work out. Thanks!
I also have all sorts of bandwidth-saving tips and configuration tips for vBulletin, if you proceed further on this. Just mail me, or stop by my Board and ask in my ATMB Forum.
Oh, and there’s a message board at http://www.vbulletin.com that might be useful as well.