I wanted to mention briefly in my blog that a few people I have spoken with over the past (and in an article I read today) have applied the YAGNI principle when deciding whether or not to implement a design pattern.  Wikipedia even mentions that there is a sort of trade off between YAGNI and the "benefits of refactoring code".

For my mind there should never be a trade off, since both principles have completely separate motivations.

The principle of YAGNI is to only implement that functionality that is required in a given story, and in my mind this, because of the disparity between the two principles, should be regardless of the patterns and practices you utilize.

Design patterns, and OO in general, are used to reduce complexity and increase maintainability through the use of recognised and proven patterns and practices for a given problem domain.  To assume that you aren't going to need maintainability and simplicity in your code base implies we could all revert to functional programming, which of course is not something anyone would advocate.