I'm sure all you coffee junkies out there experience these effects, even if you're not actively aware of them. You may just be drinking coffee and caffeine to keep you awake and alert, but you may want to consider it pre-workout or competition in order to improve your performance. I will specifically be addressing and summarizing how it improves performance for power athletes.
According to this article, caffeine use has been shown to "increase peak power output, speed, and isokinetic strength in sprint and power events lasting less than 10 seconds." In other words, caffeine is useful for anything anaerobic in nature.
The big question typically is "how much caffeine should I take?" The article recommends that for performance improvements, one should take 1-3mg of caffeine per kg of body weight (0.45-1.4 g/lb). For example, I am about 95kg (209lbs), so I would need between 95-285mg of caffeine. Anything more than that and you'll start feeling the negative side effects such as jitters, nervousness, headache, etc. that are typically associated with caffeine.
You also need to be aware of your body becoming tolerant. Similar to training, the body ultimately adapts to what you put in it by about day 5-6 if you use it consistently. The article recommends to routinely reduce your caffeine intake every 3-4 days to reduce the chances of becoming tolerant.
Lastly, timing is also important. "The concentration in the bloodstream peaks in 30-60 minutes and stays high for 3-4 hours."
So, for all you caffeine addicts, keep it up! HA! For those of you looking for an added bump in performance, consider tinkering with your caffeine intake and use. It should be a given, but ultimately, be smart and be safe!