 Usability: when we had some 
money to spend and decided that a beginner's tutorial was the most 
critical piece that we needed we hired a medium-level user to write it. 
He had gone through the induction to the system recently enough to 
remember the problems, but he had gotten past them so he knew how to 
describe them. That allowed him to write something that needed only 
minor fixes by the core developers for the things that he hadn't gotten 
right, but still covering the 'obvious' stuff devs would have