Yeah, it's real (Was there a doubt?). Went from drinking no coffee or tea 2 years ago to drinking coffee or tea every day. Generally, if I drink more than 3 cups of coffee a day for a while, I experience withdrawal headaches if I go a day without drinking anything caffeinated. Now I just drink 2 cups of coffee a day max, and routinely go days or weeks without drinking it at all.
Also, regular drinking has desensitized me to caffeine. It used to be that 1 cup of coffee would make me wired and a little jittery. 2 cups would have me running up walls. Now 2 cups is nothing, though I still don't drink coffee past 5PM if I plan on sleeping at 11PM.