Hi!
I am an OS X developer, and I have created installers both using PackageMaker and "custom installers" which are basically apps, that work as an installer for more complicated installing process that PackageMaker can allow. I also used other "installer making" software (Iceberg, Packages, Pacifist, InstallEase) that allow to have much more flexibility than an installer, created using PackageMaker (all of them output mpkg and mpkg packages - which is the same format that PackageMaker has, and these packages appear to the user as an installer icon, like any other application).