Hmm, well, I brought it up for a different reason.
The forums used to be under the www subdomain. As long as it's down, all over the web there are tons of dead links to forum posts. I'll often Google something and get a promising result from the forums, or be following a link to the forum from another site, but I can't reach it unless I manually change the domain to forum.doom9.org, which most people won't know to do.
The web server should also respond to
www.doom9.org requests with appropriate "301" redirects to forum.doom9.org. In theory, this should cause search engines to update their links, and it will help the Wayback Machine stay current, as well.