Someone working with KDE has a great open source usability blog, one of the things found was this bit about use cases and scenarios. Incidentally, this is just what I am currently working on.
Also there: The #1 Problem in OSS Usability and What I’m Going to Do About It, which Antti Kaijanmäki, another Kesäkoder, told me about some weeks ago. Though it is sad, seeing that other open source projects suffer similar problems helps keep me from going nuts :). Slowly I am becoming convinced about the critical need we have for clearly documented knowledge about our users.
Still, I guess the greatest challenge is to actually get the community thinking about users also from some other point of view than “I am the user so you should be listening to me about feature X”.