Having travelled into the U.S. from Canada over 100 times I find that by and large U.S. Border Patrol/Customs/Homeland Security agents are decent enough people. I don't have a record, but am just talking about the travellers experience.
The problem is travelling after an incident involving terrorism when security gets increased and everybody is on edge. Who wants to be the customs guy who becomes known on CNN as "the guy who let some terrorist in". That is one reason they go hyper after an incident like the Delta/Northwest flight Nigerian guy. Sure, the govt raises the security level, but the individual agents are under a lot of pressure not to be the weak link in the chain so to speak. When times are less stressful borders are more pleasant. For at least the next few weeks crossing into the U.S. will be a real pain. The Toronto Star headline on their website tonight was "Bedlam at Pearson" and the delays crossing through U.S. Customs was said to be 3 to 5 hours due to more checks, hand inspections and volume of travellers. If it takes a minute to hand search a bag, multiply that by several hundred travelers and you get several hundred minutes, which explains the 3-5 hour delays.