John Montgomery points to this interesting article on the physical effects of Coca Cola. (Short version: you get a sugar spike, one more potent than you could stand if the taste of sugar wasn't cut by the use of phosphoric acid.) 

I gave up my daily Coke early this year and, doing very little else, dropped from The Most I've Ever Weighed to Less Than I've Weighed In Fifteen Years. ~240 calories a day ~= 7200 calories per month ~= 2 pounds worth of calories. Once I learned to diagnose the "coming off the morning coffee, ingest coke" urge and manage it with a not-vastly-sugary snack, I haven't really missed it on a daily basis. I still keep a six-pack around and I admit that I drink a can before Ultimate games!