Nobody likes to read or write documentation, but it is important to have. Each framework was evaluated on the quality and thoroughness of the documentation.
YAML has, by far, the most extensive documentation. This is definitely to their credit but I didn’t find the lack of extensive documentation of Blueprint CSS and 960 Grid System to be a very big problem. I found the code itself in all 3 cases to be sufficient. For anyone interested, NetTuts has a very nice Blueprint CSS Tutorial.