I did an ESTA form online.
As I went via Dublin I checked through the border there, rather than at JFK. I didn't realise this at the time though. 2 simple questions from the border guy at Dublin to do with my work, scanned my prints and face, and he stamped me in, no problem at all. I was obviously checked over on my baggage and frisked which I have no problem with at all.
I arrived at JFK and I just handed in my card that declared I hadn't been handling cows and sheep - and that was it. They didn't even ask me for my passport.
I walked through into the arrivals lounge and wondered how I had got there without a severe check/silly questions/rudeness etc..... so I went back in and asked them where the immigration control was. They told me that the border control is in Dublin for my flight, and they don't need to do it on the JFK side.
Fantastic, I couldn't have been happier.
I caveat my story with the observation that I had seen some people had been held up 'further investigation' just before boarding, and not looking too happy. I don't know how these people were 'chosen' but I was just glad I wasn't one of them. So maybe I was fortunate.
If I had grief at immigration I wouldn't have been at all happy, I was on business and only there for a very short period of time... I can say that I will definitely go back though, partly because the experience was very untroubled for me personally.