I just came back from Dublin today. You can check out their duty free at
www.theloop.ie
THe process goes like this: 1) Airline check in counter 2) Airport Security 3) Duty Free/Food Court 4) Terminal, limited food options 5) US CBP Preclearance facility (and another quick checkpoint - shoes off and laptops via xray, but no WTMD or Nude-o-scope, they are only checking baggage) 6) USPC terminal with only 1 crappy coffee shop in it.
I am not sure how it works if you buy whiskey in Duty Free there - can you carry it on since it is in excess of 3oz?
If you're in Dublin, go down to Dawson street and hit the Celtic Whiskey Shop. Best place in town to get whiskey and they will wrap it for you should you want to check it. Also next door is Dawson's pub (one of the smallest in Dublin) - worth stopping in for a pint.
Edited to add: Global Entry is up and running. As soon as you enter the CBP area, go down the first lane to your right with the gate that says restricted area. Go around the corner and there are 2 machines there.