I drink no coffee and can do 20 hour online poker sessions like no ones business
I drink like 2-4 cups a day on avearge.
One cup with breakfast, one with lunch. Can't imagine replacing sleep with caffeine.
I used to drink 10+ cups a day could stay on porn sites and the board all night and go to work the next day...
I drink at most one per week but most of the time less than one per month. I bought my friend a cup of coffee two days ago and drank a little myself, but it keeps me up all night.