Particularly, I slept in almost all of my classes from my first classes in life to college classes.
When teachers are introducing a subject, they spend a lot of time introducing it and I get to sleep. When I wake up I've lost several of the significant bits and then I come back to sleep because I won't understand the class anyway...
So I have almost always learned by books...
The exception is the situation where the classes are subverted. You start the class with a challenge. A real-life challenge. Then, it will get my attention and I'll try my best to understand what the teacher is talking about that will eventually led me to solve that kind of problem. When they start talking about a subject from the introduction, I never know exactly what is that useful for...
I know there are others like me. For those, presenting the final solution first, could help them learning and following the guide.
You can say "you can do an application like [this] with Rails by following this guide. The application will allow you to...". Then, the reader is invited to take a look at the final built application first.
Then, the guide will explain step by step how to get there.
I know that there are other sort of guys that will prefer the traditional model, but maybe this is something that could be tried...
The problem here is that it is a bit complicated to write good guides for everyone. When I started learning Rails, for instance, I already knew a lot about general programming, web programming, databases, etc. I just wanted to know how to get things done with Rails. Someone that is starting his programming life with Rails will need a completely different kind of documentation.
Trying to get a "universal" guide for every public is a challenge at best.
On the other hand, trying to organize the guides in sections (begginer, intermediate and advanced) is not feasible in my opinion since it would require much more effort.
So, I have to tell you, specially you, Xavier, congratulations for all the hard work that have been done with the Rails documentation effort. It is a definitely hard task that has being done in the best possible way!
I take my hats off to you and the documentation team!