Whisky or Whiskey

The Scottish spell it whisky and the Irish spell it whiskey, with an extra 'e'. This difference in the spelling comes from the translations of the word from the Scottish and Irish Gaelic forms. Whiskey with the extra 'e' is also used when referring to American whiskies. This 'e' was taken to the United States by the Irish immigrants in the 1700s and has been used ever since. So what are the differences between the whiskies from these three nations?