Personally, I find caffeine to be totally inferior both as a stimulant and as a drug in general. I do enjoy the flavor and warmth of coffee, but I don't really need it, nor do I rely upon it as I take prescribed dextroamphetamine for ADHD. I'd say my daily consumption is less than 150 mg - usually only 50-100 mg... Never really cared for stimulants from a recreational standpoint, other than cocaine.
Too much caffeine and I feel irritable, jittery and anxious. Rather than enhancing my ability to focus and be productive, it usually causes just causes problems. I view it as a fairly benign drug overall, but just don't care for it.