Many thanks to Ellen for her comprehensive and careful responses, and to everyone else, too, who has posted--much good info here. I do think, though, that Phydeux has raised a point of interest: where is the line between a relaxed wilderness experience and an over-controlled, industrialized-hiking-endurathon? I have certainly used Gu and many of these products, but at some level I do feel a discomfort with using products that in some ways function almost like drugs. On the other hand, anything that can make an intense hike more comfortable and safe is certainly good. And of course SAR personnel must do whatever it takes. But, there is a point beyond which I believe that over-focusing on your "performance" and obsessive tinkering with your body chemistry, as if it were just another high performance engine, makes appreciating the total wilderness experience more difficult. (Or even impossible, because when the body doesn't "perform" as one wished, there is disappointment in its 'failure', instead of appreciation for the wilderness.) Someday I'm gonna do Skyline with a wicker picnic basket packed with Italian salami, three pounds of ripe mangos, an antique Irish lace tablecloth, and a nice bottle of organic Argentinian wine. Yes, it will take me fourteen hours. But damn will I taste good!
But seriously, I also have a longer-term health concern, which is that many of these products, especially Gatorade, contain many artifiical/chemical ingredients--preservatives, artificial flavorings and artificial colorings. I would be concerned with regularly (i.e. every weekend) consuming very large quantities (2 to 3 liters) of these products, especially in the stressful conditions of an intense hike. It can't be good for the body. It just seems to me that the lab-produced drinks and gels are questionable. If you do decide to consume endurance-type drinks during hikes, I think it's best to make your own. It's pretty simple and there are various recipes on the Internet. Or maybe Perry can post his?