C just sent me an interesting article: Can Dehydration Aid Performance
And while I agree that sports drink promoters probably over promote the fears of dehydration to sell drinks, I think staying hydrated is an extremely important part of running. Even if elite runners can deal with a greater degree of dehydration than the average runner, I think its a razors edge - and its always better to loose a few seconds for that cup of water that having a DNF because you passed out a mile before the finish line.
The book I was reading, Running Like An Animal, spent some time on water how many animals use water to regulate temperature.
Camels survive in the dessert not just because they have amazing abilities to hold huge stores of fats, retain a remarkable amount of water and are built to stay cool and shade vital organs... they survive mostly because their bodies can deal with temperatures that would kill us - not just slow us down, or lead to brain damage. They can drink salt water to re-hydrate, their bodies can function with much less water percentage than ours too. Elites are probably just a bit more on the camel side.
Granted camels need a year to recover from extreme exertion - so maybe they're passed the camel side.
For me, based on my runs in the woods, I'm going to be uber-cautious about hydration and not mess up my races. And if I do find myself dehydrated, I'll keep the article in mind and try to channel my inner camel, minus the salt water drinking of course.