Just wanted to provide a recent datapoint for flying back into the US from Dublin, Ireland. We flew over for the holidays and had a direct flight back to the US earlier this month. Dublin has US Customs in its airport, so we dealt with the process before we flew. The whole interaction took maybe 30 seconds. My husband and I went up together, I handed my US passport, he handed his Irish passport, Green Card, and Extension Letter, the agent took the letter out of the envelope, looked at it, and then handed everything back to us. Maybe it helped that we went through together -- he's been asked questions about where he lives etc when he travels alone, but we weren't asked anything this time around and there wasn't a long line or anything.