Go ahead and enjoy your coffee break.  The caffeine in your coffee just might enhance your long term memory.  Researchers at Johns Hopkins University say participants who took 200-miligram caffeine tablets after studying a series of images were better at distinguishing these same images from similar ones when tested the next day.  Senior author Michael Yassa says scientists have long known that caffeine has cognitive enhancing effects, but he says its particular effects on strengthening memories and making them resistant to forgetting has never been examined in detail in humans.