I'm not as well travelled as many gransnetters appear to be. I've only been to the US twice. The first time was about 18 years ago when we took my son and his best friend to Florida. We went via Bangor, Maine and had to go through customs there first and then again in Orlando. My husband had taken a few non-fiction books (he always does this when we go on holiday and seldom looks at them). He was rigorously quizzed about it in Maine - was he intending to work in the US? etc,., etc.. They were very intimidating.
The second time was a couple of years ago when I went with a a group to celebrate my friend's 60th birthday in New York. The customs people weren't so intimidating but they were absolutely blank faced.
Having said that, I found most of the people we met to be very pleasant and friendly, and service in hotels, restaurants, bars and on public transport was usually excellent (apart from a cruise on the Hudson where we had a ghastly meal, were charged $35 for a bottle of wine and were finally turfed off after about 2 hours to make way for the next "sitting".