Have translations checked. Nokia and translations don't go together well. Other than that, I'm not sure. It would be cool if, say, somebody who recently got the device and remembers what wasn't clear to him in the beginning could check and tell you if this one topic is sufficiently explained in the manual - nice idea, but then it's too late. You should have your documentation ready before this user buys his device. No, I really don't have a good idea here.
Second is simply by reviewing manuals if they are made available before hand. It certainly isn't the strong point of most opensource communities, but you could give it a try
i think printed guides should die- its a waste of trees, lets be honest- you dont buy a phone like this and not know how to use google or use a pdf/html/whatever help. perhaps the phone should have an specific app pre installed that updates over interent with a help search.
I think it would be amazing to have a way to link to a community-maintained wiki from the applications. That is, a help-key press launches the browser and takes the user to the maemo.org wiki page associated with that app.