Tried a Glaceau Vitamin Water today after biking home in 100 degrees. Not impressed, My grape ORS did better and had a stronger flavor. Phooey!
The vitamin water and similar (ie Propel) aren't set up to really be rehydration drinks. Not enough potassium or sodium. Better than nothing, and I love my propel, but not really set out for the weather we've been having.
By the way, these are the two products I used while deployed (no affiliation w/ either site):
http://www.tacticalresponsegear.com/catalog/product_info.php?products_id=2258http://www.nitro-pak.com/ceralyte-oral-electrolytes-50g-2-pak