I'm kinda unhappy with the latest MythBusters episode, the one about two cars smashing into each other at 50 mph is equivalent to one car smashing into a wall at 50 mph.
The way they tested the myth on a small scale was by swinging two pendulums into each other, with each pendulum containing a lump of clay and an additional weight in the back. The second weight would squash the clay, and from the deformation the impact of the smash can be visualized. It's a pretty clever rig.
My problem, however, is not with the rig; it's with the interpretation of the myth. There are two ways in which the two crashes can be "equivalent": from the perspective of the car, which is what the MythBusters tested, and from the perspective of something in the middle. Since the original myth is about a compact car being squished between two semis, it would seem that this myth should be about the latter interpretation. And in that case, I believe the crashes are, in fact, equivalent.
As an educational show, I think MythBusters should have at least covered this other scenario, and shown how the "myth" is more of an interpretation issue.