Most hardcore, really in to it, endurance athletes i know (and that is 100's) will only reach for a Gatorade, et al, out of convenience during a training session or race. Post race re-hydration though most people generally agree, myself included, that Pedialyte delivers a better result than marketed sport drinks at getting electrolytes back into the system.

Just yesterday I was sent a link to a new book by Dr. Tim Noakes, the foremost authority on running in the world. His book is

Waterlogged: The Serious Problem of Overhydration in Endurance Sports
at 429-pages and his level of research it is not light reading but you will find it will set the tone for thinking for the next few years.

A friend of mine who did Ironman New Zealand recently said that they were very concerned with over hydration and advised against it for the individual as well has providing less water stations on the course. End result was they had less cases or hyponatermia (an electrolyte imbalance in the body usually from too much water being put in it)