Those are usually 2-3 servings poer can, so if you drink two you're drinking 4-6 servings. I ride with a lot of randonneurs and a RAAM competitor, and they're of the opinion that if you ween yourself off caffeine, judicious use of it at the right time can really speed you through your sticking points. I've started to de-caffeinate myself over the last month, only drinking it when I need it - so far I've found them to be right.
I also noticed that my sleep quality has improved dramatically, btw.