There's a wonderful article on LWN.net at the moment, 'Usability and adaptableGIMP.'
It details the work of Michael Terry, a human-computer interaction expert, into an alternative interface for the GIMP. This interface is task orientated and constructed based on an analysis of search engine queries relating to the image editing program. Once a user selects a task, a new tool palette is presented to the user with the tools needed to complete the task presented in the appropriate order. It's something of a 'built-in tutorial,' although it feels like far more than this.
There are packages available to try here.
It's a fascinating read, and the article's introduction alludes to some other work done by Michael Terry that sounds just as interesting - in particular, 'Textured Agreements' which was an effort to get more users read and understand End User License Agreements (EULA).