I've found ActionCaching to be unusable in its current state when trying to cache multiple formats (eg caching both /people.html and / people.xml). I have a patch that I'd really like to see in the 2.1 RC - http://dev.rubyonrails.org/ticket/11184 / http://github.com/jdelStrother/rails/tree/caching
I've been running this in production for a while without problems. Let me know if there's anything more I can do to convince you it's a good idea.
Jonathan del Strother