Petr Pisl’s article about the --userdir has a paragraph you should read first: “I don't use installers, I always download NetBeans as a zip file. These are available on nightly build download page, where OS Independent Zip item in has to be selected in the Platform combobox. …”

[http://blogs.sun.com/netbeansphp/entry/userdir]

The assumption here is that not using the excellent installer for NetBeans makes using the --userdir parameter easier. I could be wrong about this…