Only been once, but yeah, not a great experience! I was coming into the US overland from Canada, pre-9/11. The guy was really hostile, I felt like a criminal. He ended by ordering me to go and withdraw a certain sum of money from a cashpoint and then when I went to do it, sneering that he hadn't meant me to actually do it, he just wanted to know if I could.
By contrast, coming into Canada from the UK some months earlier, with barely any money, intending to work but with no job lined up, they couldn't have been nicer. I had a citizenship card with a photo of me as a baby (!) and they called their colleagues in to have a laugh about it, in a nice way, saying they could see it was me, go on we'll let you in 