Via a MacRumors Forum thread, I've just discovered a brand new OS 9 site called Mac OS 9 Lives. It's still building (in fact, when I wasn't looking they added a new Digital Audio Workstation section), and it has a user forum, so go over and check it out.
Also of interest are a few other OS 9 links:
OS9.net (some of their links may be old)
68k Macintosh Liberation Army Forums
Old Mac Archive - Abandonware for pre-OSX Macintosh computers
Macintosh Garden - Celebrating macintosh abandonware!