How do I set the default file permissions for GUI apps in Lion?
I think you have done what you could; the umask really is 077. When programs create files or directories via the mkdir system call, they specify a mode. The file or directory ends up with a mode which is the specified mode, but with any 1 bits from the umask cleared. So in all likelihood, the GUI programs create their directories with a specified mode 755, and if so, there is no change of the umask that will help. (If all GUI programs do this, it is probably because they all use the same library to create the directories they want to exist.)