I really need coffee after lunch and preferably a second cup in the afternoon (espresso, of course
) or I lose all energy and what little desire to keep doing the necessary things I have left.
As for the effect on SP, it does make me a bit more anxious, but at the same time more willing to put myself in social contexts, and more talkative and less depressed than I would be in my "default setting". All in all, benefits outweigh costs for me.
For those who drink so much coke and similar stuff, I think you should try to switch to coffee for your caffeine intake... If you drink two liters a day or so, it's like living on a diet of sugar (2liters (six cans) of coke: 800 calories, average daily intake: 2000. That means about 40% of the food you eat daily consists of sugar!) It's going to give you diabetes in the long run!