I read about it and I thought it seemed pretty cool. Of course, it also sounds too good to be true.
Really, though, I think it would be prescribed to people who have various illnesses or conditions that make it difficult to exercise or something. I would use it. I have CP. It's starting to cause problems in my lower extremities re: loss of muscle tone and whatnot again, not to mention fatigue due to the overcompensation that my other muscles have been doing for the last 25 odd years. My feet are curling inward and everything, and there's nothing I can do about it because I lack the ability to control certain muscles. It's weird and unpleasant -- not to mention gross-looking. It makes little things like walking difficult and scary. It makes other (necessary) things like working really exhausting. I think something like this drug, accompanied by traditional PT and bracing and stuff, could really help someone like me to stay strong and active by taking some of the edge off of the muscle weakness and fatigue.
That's just one of the potential applications. For the first few years, at least, I think the CDC would keep close tabs on it and try to use it judiciously. Then, yeah, it would become a diet pill. But so what, if it works? Exercise in a bottle is a great idea!