A little known fact about coffee is that dark roasts contains less caffeine than the same beans roasted lightly. This is something to consider for espresso which normally uses a heavily roasted bean to achieve that punch you want after a demitasse of the thick stuff. On the other hand espresso is sufficiently concentrated to make up for any degradation in the caffeine content due to roasting...

While working in a university astronomy department, I ran into a pair of graduate students who were heavily into experimentation with coffee as a drug to aid them staying awake for long nights. They found this lightly roasted african coffee that just gave me the shakes, and I was no lightweight in the caffeine department at that time. Ten minutes after imbibing, I had to use one hand to steady the other while typing away on my terminal. They had also presented the brew to a relative coffee virgin, one of their professors. It was a lecture to remember.