This isn't just an issue with SilverStripe...it seems all the open source CMS products I've checked out recently (including the big ones like Drupal, Joomla and CMS Made Simple) have terrible documentation. Generally they suffer from the "written by developers, for developers (that sit in the next cube)" problem.
E.g. the docs.joomla.org wiki is a sprawling mess of random user input, with little fitting together. Cohesion and quality are the big factors.
It seems that SS could make documentation and tutorials a serious priority - it would be a nice strategic advantage over all the other free CMS' out there. SS is already half way there with the current tutorials and documentation...just need some good technical writers to fill in all the gaps, keep things up-to-date and reform the current stuff in terms of language and unnecessary jargon.
Documentation can be made a critical component of the product, with business rules supporting this. For example, before any new version is released all documentation must be up-to-date in line with the new release, while still maintaining backwards support/compatibility with older versions - and this must be rigorously checked/enforced.
IMHO the aim should be to create a graded entry system whereby potential new users can "slot in" where they feel comfortable in the structure of the tutorials/documentation. Starting at the very basics of CMS principles and even basic PHP tutorials as it relates to SilverStripe.
I really like the structure you guys have at present of different Levels of documentation - it's a great concept.
I'm Looking forward to seeing what can be done :)