I'd like to revert to the default… defaults, bringing them back to where they were originally or, more specifically, where they would be for a new user account or new system. Is this as simple as using
defaults delete on the appropriate domain and key?
Yes, usually you can just use
defaults delete. If for example you have run
defaults write -g NSScrollAnimationEnabled -bool false, you can undo the changes by running
defaults delete -g NSScrollAnimationEnabled or
defaults write -g NSScrollAnimationEnabled -bool true (and by reopening applications to apply the changes).
Even if the preference key had some value before you used
defaults, it shouldn't matter if you delete the key. It is generally safe to delete preference keys or even complete files, and they can usually be recreated by OS X or applications.
The property lists modified by
defaults are stored in directories like
~/Library/Preferences/ByHost/. You can edit a plist in a text editor after converting it to XML with
plutil -convert xml1.