I got queried rather heavily in ORD last year after 3 trips (2 business, 1 pleasure) with bizarre questions like "how do they feel about you being out of the office so much?" And "can you tell me the dates of your last visit to the USA?" (No, of course I bloody can't, I was travelling abroad weekly at that stage...)

Never actually not got through, though. And now I have a passport without visas for Pakistan, Uzbekistan, Morocco, Malaysia et al, I get questioned a lot less.