I'm sure most of you big whisky appreciators know this, but for KCW and the newer tasters, here's a tidbit I've always found interesting:

Something about Single Malt that is fun to pay attention to and see if you can catch hints of the flavor: all single malt is aged in casks that were originally used in the making of other spirits and such. Distillers purchase used barrels from wineries, distilleries of other spirits, etc., in order to give their product an extra slight flavor - and in many cases you can taste that in the product itself. Good stuff.

Balvenie reveals some of the casks they use, for example, on this page. Sherry, Port, Rum, and others make up their aging casks. Pretty neat.