Tacit knowledge

At the ECSA conference there was a lot of talk about tacit knowledge and the importance of tacit knowledge when architecting systems.
I completely agree that one thing that differs an experienced (and productive) architect from a fresh graduate is is the amount of tacit knowledge the former possess. However I thought that in the discussions at the conference there was some confusion of what is exactly meant by tacit knowledge.
On one hand there was the view that tacit knowledge was simply the architectural knowledge that was not documented, i.e. stuff that only resided in the peoples' heads. To improve the management of this is mostly a question of capturing it in the right form and with the best tools.
On the other hand one sees tacit knowledge is such knowledge which is difficult to express using language, which is the tradition I'm used to.
In order to capture the latter type of tacit knowledge it is not just a question of having the time to do so or the right tools. The difficult part is for the person having this knowledge to be able to formulate in in such a manner that he can express it.