You know...they actually work fairly well. It really depends on what you use your laptop for, I think. If you usually use your laptop on a desk somewhere, or you don't mind lugging around the extra weight with the cooler, then it is a pretty good investment.
They do drop the temperature of the laptop quite a bit. If nothing else, they lift the laptop up off of the surface...which is usually what most laptops need anyway! Most overheating issues that are not caused by massive hardware problems are solved by adding something like these pads.
I would say these are worth the investment.