For those wondering about my exam performance, I meant giving it up for approximately 3 weeks until my finals, at which point I may allow myself to backslide.
The 5PM comment made me giggle. I try to stay away from caffeine after about 10PM, which is probably comparable to your 5PM.
For me, there's quite a variety of influencing factors. I'm from a farm, with a well. I shan't even start in on the city water after it comes through the pipes in my dorms, which are from approximately the protestant reformation. I guess you could say I'm a snob about bottled water, it tastes "flat" to me. It's ok, but doesn't taste good, as I'm accustomed to water tasting. I just tend to drink a LOT, and it's easy to buy large quanties of diet coke and dr pepper. I also just plain like the taste of coffee, and it's nice when it's cold out, or to make a pot and stick it in the fridge when it's cold out.
Granted, there are possibilities such as juice and gatorade, but have you seen the sugar content of those? Sugar makes me jittery, and it doesn't take very much, whereas I'm fine with all the caffeine in the world - I hit my baseline needed to function, and anything past that doesn't do anything beyond normal functioning to me, or at least what I've become accustomed to as normal functioning. I'm dreading the withdrawal symptoms. I'm going to see my coffeepot every morning, just staring sadly at me, looking forsaken and lonely. And my coffee cup - empty, dejected, despairing.