The Ative guys has a blog with a lot of insightful development project gotchas. This one, in particular, made me chuckle.

Although I've never had to introduce bugs on purpose into a system, I think this is is a very elegant solution to the described challenge.

Update: After thinking a bit more about this, I just realized that from the description of the solution, it sounds like an application of the Decorator pattern. No wonder it's so elegant :)