I believe that Dublin pre-clearance is now the same as Shannon Airport. At Shannon you go through regular Shannon airport security and then you enter the pre-clearance area and go through US style security (without the yelling) - shoes off, etc. Next you come to the CBP booths, where they do the immigration check and also show you a CCTV picture of bags and do the customs check. At this point they can secondary your luggage and have it sent to another area if they decided it is necessary. Also, they ask about food, etc., and can send you to the agriculture inspector who is also there. (We got nailed by them here a while ago for having bacon sandwiches for the flight as they consider when you go through all this pre-clearance you are in the US even though you are in Ireland, and so cannot bring bacon in with you).

After all this you go to the Gate area to board your flight, and arrive in EWR at a domestic Gate. No further security checks at EWR.

Note that CDP also has a beagle and handler wandering around the lines to the CDP booths and they also wander around the Gate area while you are waiting to board the flight at Shannon. They seem paranoid about people having their own food.

The whole procedure is a little more invasive than at EWR just because they are doing all this for only one flight , but it sure saves time at EWR, but costs you time at Shannon as the whole check-in/clearance procedure takes longer.