Developing Intelligence has a fantastic post on what pharmacology and neuropsychology has told us about getting optimally wired on caffeine.
In small amounts, caffeine boosts mental function, and the article looks at scientific studies that have told us which are the optimal doses, which psychological abilities are most affected and what you can take with caffeine to modulate its effect.
Obviously, caffeine has its health risks. Psychologically speaking, even everyday doses run the risk of withdrawal symptoms and have the tendency to increase anxiety, so as with any drug, it’s important to educate yourself so you can judge the risks for yourself.
The Wikipedia page on caffeine is wonderful, so it’s a great complement to the fantastic round-up of stimulation-related tips from Developing Intelligence.