Lambda the Ultimate

Hi,
we are currently working on the design of a controlled experiment, where we hope to measure a benefit of dynamically typed programming languages compared to statically typed ones.

Could anyone of you imagine concrete situation, where the static type system is more an obstacle than a helpful tool?
To clarify my intent: I do not want to start another "which one is better"-discussion, but hope to get concrete (code-) examples of situations where dynamically typed languages are superior.