Just want to clarify this abit.
I have been flying to America from Dublin on a regular basis for over 15 years. USA Preclearance is ONLY in Terminal 2. Only airlines which fly direct from Dublin Terminal 2 to any airport in America will have USA Preclearance.
The airlines which depart from Dublin Terminal 2 are
Aer Lingus
American Airlines
United
Etihad Airlines
US Airways
Delta
Emerites
Ethiopian Airlines also fly to America from Dublin BUT they do not fly from Terminal 2 and do not have USA Preclearance. Ethiopean Airlines departs from Terminal 1 Dublin airport.
USA Preclearance is located in the lower level of the departure gates in Terminal 2. When your USA flight is called for boarding, there are 2 stages. The first stage is that you will be called for USA Preclearance . You go down the escalators from the shopping concourse to the regular departure gate area. You will then big signs directing you down to the lower level for USA Preclearance.
There are 2 stages here. The first part is where you show your boarding card and passport to an agent. You will then go through a second security screening, you will need to take out any electric items, laptops, tablets etc and then walk through another boidy scanner. The second part is after the body and bag scanners. You are then directed to The USA Homelands Security area. There are self service machines and normal USA Homelands Security Agents. This is where you get your passport stamped and you are technically in America.
Once you have your passport stamped you go down to the departure gate areas. There are limited food and shops in this area. Its mainly a bar / cafe , toilets, a sandwich kiosk and a WH Smith kiosk.