Tapeworm said:
			
		
	
	
		
		
			What does then Frank? 
Hmmm, wonder how they quantify effort in all those cycling studies? 
If only there was some way to measure the effort of the cyclist!
		
		
	 
The issue is not whether measuring power can be useful, it can be particularly useful in scientific studies of cyclists. The question becomes whether having that information can be useful to the athlete to improve outcome from what could be achieved before this information was widely available. 
While it is generally assumed that because this measure of effort is more precise than say measuring HR or the subjective perceived effort that improved outcome would be the natural result. But, this has never been proven scientifically. In fact, the only study that I know of that has looked at this question found no improvement. 
Therefore, from a scientific perspective, the use of a power meter (dare I say gimmick meter?) for training or racing is no better for improving outcome than using all sorts of stuff like nasal strips, Q-rings, power bracelets, PowerCranks, etc. All of these things may have some benefit but it has yet to be proven scientifically.
Take your car. It is possible to measure engine power output real time and show it to the driver. But, no car manufacturer makes that available to you. Why? Well, what would you do with it? Of more importance for everyday living is what your fuel economy is or how much fuel is in the tank and that is generally available. But power? Not even in the race cars.
The potential for something being useful is quite a bit different from it actually being useful and having been proven useful. Unfortunately, in sports, much of what we do has never been proven scientifically to be effective as there are simply too many variables or benefits come too slowly to be easily studied in a controlled setting.