A wide variety of sites exist with arch information. For example:
Tom Lord's Low Budget Arch page has a wealth of information ranging from information on TomLord, the lead developer of arch, to a really nifty tutorial.
Savannah hosts the arch bugtracking system.
SourceControl.net hosts a mirror of all known public archives and their statistics.
Arch of course has a Freshmeat page.
The former Arch wiki, currently lacking administration.
The Rhythmbox project has a good page on Arch usage.
OpenACS developers sometimes use Arch. Using Arch with OpenACS OpenACS is a web development toolkit.
* http://www.thecodemill.biz hosts logs of the #arch IRC channel.