Evidently, whether you chose light roast or dark roast coffee can affect the level of caffeine that you are drinking. The first time I had even heard of this, Thor and I were trying to check out of a motel in Radium but the clerk talked our ear off. I commented that I liked light roast coffee better, because it doesn't taste burnt to me, and she informed us that she'd heard that the lighter the roast, the higher the caffeine content, and the darker roast coffee's have less of a caffeine content.
So I decided to look it up, and it appears that it can be true. Of course, this varies with the actual quality of the bean itself and some very high quality beans aren't as likely to lose their caffeine as they are roasted. But lots of them do. And a quick side note, did you know that coffee manufacturers roast their beans to hide the crappy quality that they are, so the darker the roast, the less confidence they might have in their actual bean to begin with. This, of course, isn't always the case, but it appears it's most often the reality (aside from some totally high quality beans found around the world).
The other factor on caffeine seems to be how quickly the coffee is processed. A slow drip (conventional coffee maker) that takes longer to make will be higher in caffeine than something that spends less time in contact with the beans, such as espresso, believe it or not.
So the next time you are ordering a dark roast with a shot of espresso to stay awake, consider a nice mild light roast coffee, slow dripped, the traditional way rather than a Keurig type of thing that only takes 1 minute to brew.
Here's just one little article I read about it as I did my quick topic research. Interesting.