I guess I'm fortunate--I never got roped into the whole "morning caffeine" thing. It helps that I can't stand coffee.
Overall, I try to keep to 1 or 2 cans (or less) of soda per day, which I usually have in the evening, and I've rarely had trouble sleeping. On the contrary, I've occasionally grabbed a caffeinated soda before bed or when I have trouble sleeping because it seems to help me sleep.
The same thing happened on my last long haul from Texas to Michigan, when I tried caffeine pills. The first one worked, but the rest didn't seem to have any effect, and I just pulled over at a rest stop to sleep. I still wonder whether the first one was a placebo effect.
I don't get headaches or anything from not having caffeine, but I really like the taste! Last week, I didn't have any soda all week, and then sat down with what I believe was the best Vernor's on ice I've ever had on Friday.
I have more problems with my blood sugar doing crazy acrobatics if I eat/drink too much sugar. I'm not diabetic, but I do occasionally get weird, dull, long-lasting (but not too painful) headaches if I consume too much (or too little) sugar (but I guess that's probably just a normal effect of being hungry in the latter case).
Go figure.