The listing, 12 pk (45 mins) DewXP Points - Modern Warfare 3 has ended.
DewXP, as it's called, will see Mountain Dew exchanged for experience points in Modern Warfare 3. Drink a 20 oz of Mountain Dew? That's 15 minutes worth of double XP. A 12-pack equals 45 minutes, a Wal-Mart 20-pack equals 90 minutes and so on. The full breakdown is over on the official rules page