Sports drinks may be a waste of money for most people in most situations, but they aren't harmful, and sometimes can be better than plain water for non-elite athletes as well as olympic class and above.

Sports drinks as I know them basically contain two things besides water: carbs (ie sugar) and electrolytes. (Are there really "sports drinks" out there containing caffeine?)

Any source of carbs will work as well as a sports drink, but as M_M has posted, sometimes liquid sugar is easier on the stomach than a solid source. I like dilute Gatorade for long runs in hot weather too, but for canoeing, I just eat a handful of gorp every half hour or so.

The electrolytes' main benefit (imo) is that they make hydration more efficient: water gets transported across the walls of the small intestine into the bloodsream faster, so you don't feel so bloated when you're trying to pour gallons of fluid down your throat. On my recent 10+ litre day, I wished I had Gatorade or something similar with me, because a lot of the time I felt I was forcing the water down, almost always drinking even though I didn't feel thirsty.

I think I'm as cynical as anyone here regarding marketing gimmicks, but remember that the first sports drinks were developed with no commercial applications in mind. Gatorade was invented at the University of Florida solely to help their football team win more games (hence the name). It was only later when its effectiveness became well-known that it was marketed to the general public.

Are one sports drink's electrolytes better than another's? Well, they all claim that they are. Maybe this is where elite athletes might see a difference.