Stéphane Sudre is is the process of writing a how-to on distributing and installing an application using Apple's Installer.app and packages.
This is still a draft, but the information it provides is already very useful to anyone who wants to distribute a Mac OS X application that requires a specific installation. It's also very clear and well written.
I haven't got a need for using PackageMaker so far, as all the apps I wrote can be installed with a single drag 'n drop, but I didn't think that creating a package was that complex!
So thanks and bravo for this How-To, Stéphane!