How much of that is placebo? i.e. "You're doing things because you know you're taking something that helps you do things?" Productivity comparisons with a placebo haven't been conducted yet, but I'll bet it will be rather underwhelming as a motivational agent. Especially when you compare it to other stimulants like Coffee, it will sound even less miraculous.
The silver bullet of psychopharmacological brain-enhancement hasn't been found yet. That's the holy grail.