I find this model really helpful when working with teachers to help them implement a range of technological solutions in schools.

Here is the link to the film I made for iTunesu 

What is significant with this model it that it makes it ok to know that there are things in the set up of a package that need to be addressed at the start but most users do not need to remember any more than the fact that it can be done.  The ‘known unknown’ model works for this – you know it can be done but there is no need to remember how.  In other words – it is ok for some things not to be an unconscious competence.

Here is Donald Rumseld’s take on the whole idea.