Time to clear customs in Dublin

I believe they suggest three hours, and I would abide by that. You have to check your bags, go through security, and then go through US customs before going to your gate. I have had security be as slow as snails in Dublin, and I have seen the customs line backed up a good ways, too. I know the first time we flew out of there, we thought we had a lot of extra time. But just a few minutes later they were calling for boarding!

I know we are talking "apples and oranges", but in Shannon the whole thing took about 10 minutes for our 9 am flight out. In fact, we could not get our boarding pass until two hrs prior, because United did not open until then. We cheated and popped by the airport the night prior and asked questions at the "Info" desk, so we knew when to arrive, where to drop off our rental, etc.

Be aware some flights that used to clear US customs in Dublin now do not. Double check yours.

How would I go about checking whether or not my flight clears customs in Dublin?