My MacBook Pro is setup with two user accounts: one for personal and one for work. This is certainly not my setup of choice, but if I want to use my own MBP (which is retina) at work then I have to abide by this rule.
Anyway, this setup caused an issue when I went to do something that required Homebrew. After a little research and testing Leif Hanack had the best answer. All it requires is a group that both users are members and then change group permissions on
/usr/local. While I have not done so myself, this methodology should work on other items (i.e., iTunes library) I wish both accounts to have access.