While the sherry-cask discussion is ages old, this information actually DOES add to the conversation. If one wants to be Machmir and avoid sherried whiskies, they are limiting themselves to a very small number of widely-sold bottlings (Ardbeg 10, for one), and other single-cask bottlings that use NO sherry casks in the aging process (i.e. all ex-bourbon casks). What people don’t realize is the information provided above: that even those bottlings that are not WHOLLY aged/finished in sherry (and other wine) casks, do have SOME AMOUNT of sherry-casked whisky in it.
How is this so? It is because of a process called vatting. People assume that they just pop a tap on a cask and then fill bottles to be sold. However, in reality, what the distilleries do is combine many many casks together to achieve a desired taste. The casks may be different ages, and the number of years stated on the bottle is the YOUNGEST whisky in that vatting (i.e. in a Glenlivet 12, there may be 18 year old whisky in there). If they did not do this, one bottle of Glenlivet 12 could taste wildly different from another bottle; obviously, the distilleries want conformity. For example, Balvenie 15 is a single-cask whisky, and those with discerning palates can taste differences between them.
So, the moral of the story is that more than 95% of the whisky on the market has some sherry-casked (or other wine casked) whisky in it, and for those that REALLY want to be Machmir, they should not just avoid whisky stating that it is wholly matured/aged in sherry casks, they should avoid all whisky unless the bottle states, or they have some other confirmation, that the whisky is wholly aged in ex-bourbon casks.
For those interested, I did a two-part piece on this topic on my blog some years ago.
http://alanlaz.blogspot.com/2006/06/kosher-whisky-part-i-production.html
http://alanlaz.blogspot.com/2006/06/kosher-whisky-part-ii-sherry.html