I agree whole-heartedly with the point about post-validation. I work in the field (EC) and the first dozen results you get are usually instances of the algorithm finding where your model or your assumptions are broken. For that reason the "On the Origins of Circuits" link posted in another comment is a really bad example. The results are total garbage because there was no model at all, just an actual physical FPGA. Models are great because they abstract away the effects that you really shouldn't rely on in your design. With out a model, the FPGA optimization gives us an answer that's only valid for one particular FPGA, at a particular point in its lifecycle. In fact, this might be why software optimization breaks --- nobody's figured out how to abstract away the irrelevant effects.