As someone who writes documentation for Ubuntu/Kubuntu and also has worked on The Official Ubuntu book, I would agree that documentation is the most often forgotten part of a project.  Too many times the developers of a project will put in shiny new app X and then forget to update those who write the documentation that shiny new app X is now the default app and needs to be used.   (Change app to feature and you have the same problem)

One of the great things about the Ubuntu/Kubuntu/etc world is the hard freezes that go into effect that allow people to create/change/modify the documentation before the release.  Then the documentation is frozen for translators.  While it often times provides for a great flurry of commits at the end, the freezes strive to solve the problem of shiny app X sneaking in at the end.

I would echo someone's else thought that Open Source software has some of the worst documentation (if any documentation) out there.  People volunteer to create something new, not document something new.  THere are some great examples of Open Source documentation (GNOME, KDE, Gentoo) but a greater number of terribly documentated products.

Jonathan