yeah this might be apple "conceptual" method but it seems in practice applications (lately?) are preferring to use ~/Documents as the catchall for libs,user created docs, examples, etc.
so processing, for example, in ~/Documents has folders:
examples
libraries
modes
templates
tools
similar for arduino although default install online has ~/Documents/Arduino/libraries
now that I am looking I even have an "Adobe" folder here where it looks like is stored all presets, user preferences, logs etc. AND in they un-typically install plugins/libs in /Applcations/Adobe */Plugins
there are prob many other examples of softwares throwing lib folders all over OSX
processing/arduino also make folders in ~/Libraries but they seem to be only preferences...
cheers
m