This article is from the Running FAQ, by Ozzie Gontang with numerous contributions by others.
(Paulette Leeper pleeper@wtcp.DaytonOH.NCR.COM)
I find the CAFFEINE in soda to be irritating and DEHYDRATING, so, IMHO,
drinking soda with caffeine (regardless of whether or not it contains sugar
or aspartame) defeats the purpose of quenching thirst. It's much like
drinking beer to quench thirst... it FEELS good, and TASTES good, but as a
mechanism for hydration, it does the exact opposite.