So I finally caved in. There's now a dedicated Rails mailing list at http://lists.rubyonrails.org/mailman/listinfo/rails.
If you're looking for help with Ruby on Rails or any of the components (Active Record, Action Pack, Action Mailer) that'll be the place to post. I think there are already some 50 people on there.
You can have a look at the archive for October too:
http://one.textdrive.com/pipermail/rails/2004-October/thread.html
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David Heinemeier Hansson,
http://www.rubyonrails.org/ -- Web-application framework for Ruby
http://www.instiki.org/ -- A No-Step-Three Wiki in Ruby
http://macromates.com/ -- TextMate: Code and markup editor for OS X
http://www.basecamphq.com/ -- Web-based Project Management
http://www.loudthinking.com/ -- Broadcasting Brain
http://www.nextangle.com/ -- Development & Consulting Services