In the folder Output\Preferences. You can make a copy of your preferences simply by copying the entire folder.
In the folder Resources\Preferences. You can make a copy of your preferences simply by copying the entire folder.
In the folder Resources\Preferences.You can make a copy of your preferences simply by copying the entire folder.
In the folder Resources\Preferences. This way you'll have seperate preferences for each version of X-Plane if you have multiple versions installed. You can make a copy of your preferences simply by copying the entire folder.
In version 6.06 the preferences are named
In version 6.70 the preferences are named
with a couple of other changes along the way. You get the general idea.
Version 5.54 used an additional preference file, X-Plane Joy.prf, that is now obsolete. There are additional preference files used by PlaneMaker, etc., with similar names.