well, it has been noted that even the smell of coffee can produce a heightened alertness & wakefulness in habitual coffee drinkers. that is to say, that with a strong enough conditioned-response, the body can mimic the caffeine-high before caffeine has even entered the system.
it would be interesting to do a double-blind study on heavy coffee-drinkers as to whether they can distinguish the difference between decaff and regular coffee when not informed, or misinformed.
a similar study on wine aficionados has shown that cheap wine served from an expensive bottle will be perceived as being much higher quality than when it is from it's own bottle. said aficionados report enjoying said wine much more, and being unable to distinguish the incongruity when presented with a misleading label.