Drupal is a development framework for people who know PHP and know Drupal, one step more than a pure development framework
Another start to a multi-part posting, this time working in on something that took a little longer to occur to me than perhaps it should. Drupal has a big learning curve for anybody who needs to do custom development. Drupal is often described as a cms that is moving (or already moved) to being a development framework. To use Drupal as framework however requires a good knowledge of Drupal (duh obviously, but bear with me).
Development frameworks are typically built on top of a programming language. So for example you may be a PHP developer who picks up a new framework built on PHP or a Ruby programmer who picks up a framework built on Ruby.
Development frameworks are typically built using well known design patterns. The MVC pattern being a prime example (often mistaken by recruitment consultants as an actual framework in it's own right). To this extent experience with one or more frameworks can boost the uptake of a new framework. For a developer or team that has experience with relevant technologies, the programming language and some of the patterns used, new frameworks can be picked up quite quickly.
Drupal as a framework
To use Drupal as a framework you need to know Drupal, you need to know PHP, you need to know about a lot of contributed modules that extend Drupal's core technology, you need to know about the changes from earlier versions (to help make sense of some of the documention that is there) and you need to have spent time learning where to find help and further information. Drupal has nothing to compare with the documentation of many other frameworks.
Granted that pure frameworks don't do anything out of the box themselves and that Drupal is primarily targeted at people that will not program with it, however it seems the overhead for even an experienced programmer to pick up and start running with Drupal is still too high and the patterns you need to help you navigate it too obscured.
What do you think about the Drupal learning curve?