If you've been to a whisky tasting event or have a well stocked whisky cupboard at home you will know that after you've had a few different whiskies the response of your palate starts to change. This can be reduced by drinking water or perhaps eating a plain water biscuit between whiskies. I'm not sure of the scientific explanation but there is a phenomenon known as olfactory fatigue during which the normal ability to distinguish a particular odour is temporarily lost.
You may have noticed that after eating something very sweet, say a pudding at the end of a meal, the wine that you were happily drinking with your main course starts to taste too acidic. It's as if you can no longer taste any of the wine's sweetness. You can sometimes notice a similar effect when tasting a number of whiskies back to back. It can feel as if your taste buds are experiencing fatigue or that they have become so saturated by, say, a sweet whisky that your response to sweetness becomes muted. Other flavours such as salt, bitter and sour start to come through more strongly. This odd bit of biology can reveal to you flavours which might be otherwise too mild or weak for you to initially detect. Laphroaig in their sensory tasting event at this year's Islay festival (2010) employed this concept to good effect, by matching their whiskies with small portions of blue cheese (highly salty), smoked fish (mimicking peaty phenolics) and chocolate (highly sweet) some of the key tastes in their whiskies were knocked out in turn.
It's worth bearing in mind that what you've just tasted can change the flavour of what you taste next. This can sometimes account for why you may love a whisky one day and be indifferent to it on another. The truth is there is no objective truth. or something.