I'm hoping to lobby for IDEA-100680...
On Mac OS X the idea.properties override mechanism doesn't work because of some typo somewhere in the idea source where IDEA looks for "idea.properites" (see the typo) instead of the proper filename. (The bug above has all the details.)
This stack overflow (answered by JetBrains' CrazyCoder):
has plenty of comments showing that indeed it's broken for peeps for idea.properties.
The bug is so trivial it appears to have been fixed already, but it never got included in an EAP so far.. and with 12.1RC1 out, I'm really hoping to get it included before we have to wait to 13.
Pretty please? With sugar on top? :-)