One of the biggest complaints with Rails is the lack of good documentation. Unfortunately, Rails is still very young, and the talented developers are either extremely busy with their jobs, or being paid to write books. The #caboose folks have started a Documentation Drive to raise $5000 to hire a professional to enhance the documentation. If you use Rails professionally, you should really consider chipping in for the benefit of all Rails developers.
Update: Thanks to some very generous contributers like FiveRuns, Fingertips, Reforge, and cdbaby, the fund is now over $13,000.