I think this is everyone's biggest issue with Open Source. It also seems to be the "least wanted" by programmers working on the projects.
As a professional tech writer, I've offered my services to a few open source projects that I'm a fan of but feel have a major lack of documentation. In each case I've been rejected. I've basically been told, "Our programmers write all of our documentation." The existing documentation in each case might as well say "just figure it out." I've offered GUI design in the past as well. Lets just say this didn't go over well at all.
It seems that Open Source is a programmers club more than anything. It's a real shame. There's so much talented work going into the development of the software that it would be nice if the rest of the work (documentation, gui design, graphic design, etc) was doled out to the experts. There's nothing wrong with admitting that you're not super talented at everything.