Hobby software being what it is, there is no centralized place to have documentation. Everyone turns to search engines, which means that user-contributed documentation can go anywhere online.. and it doesn't matter where.
This means that any project which attempts to centralize user documentation will be forced to reach out onto the net and cache their contributions from outside sources. freedesktop.org is our timely example! (wmctrl)
If the original user documentation is updated, or new documentation is created, then that central resource goes out of date.
But is there hope? Not at all! =)
An enthusiastic user can only hope to contribute directly to the project. Failing that, they have private notes or hopefully blog.. and that's one big mess.