I'm frustrated with open source projects that do not give emphasis to accurate and full documentation. I'm sick of watching lead committers run to O'Reilly or Wrox for book deals only to leave the project with often incorrect documentation. I'm not going to single any projects out, but it seems that there needs to be an effort on the part of some organizations to try to encourage people to contribute to documentation.
The alternative is ending up with a situation where one must pay for documentation. Look at JBoss 3, it's technical impossible to use JBoss 3 without spending $10.00 for the documentation. Want to see a complete manual for Log4J? You'll have to pay $49.00 to Flashline to read it. Seems like there is a general movement towards open source projects with paid documentation.