There was one time last year where I got detained for 8 because they didn't believe that a college dropout could run a company, even calling me "full of shit" at one point. They had my computer and went through my email one by one asking me to cite specific dates of employment at 3am in the morning.
They ultimately rejected me on the basis that I got one of the dates wrong. Can't say I've ever had a good experience with any US customs official.