The effect wears off quickly, eventually your efficiency will level out and if you stop drinking coffee/energy drinks, your productivity will be lower than ever before. But people love drinking energy drinks and coffee, because it's cool!
Edit:
While I agree that energy drinks and coffee can be used for a quick boost in productivity (never worked for me), I believe that the potential advantages of these products are being ignored and they are simply used to make a statement about your identity. If you need extra energy EVERY single day, coffee is not going to work, actually, nothing is going to work in the long run. Caffeine is just another useless, albeit cool, addiction like nicotine.