I'll concur with that, I'm a dual UK/CDN citizen and I've never had a really bad experience with US customs . I'm upwards of 50 or more crossing over the years from different ports of entry, New York Michigan Boston Maine Miami Atlanta and a few others, met a few less than jovial officers but never been over the coals by Uncle Sam. Crossing the border on my sportbike I've even been waved thru by the officer without even raising my extremely dark visor. Granted this was pre 9/11 but IMHO US immigration was far laxer than Canada's ever was, as strange as that seems.
In Canada I get harrassed almost everytime, especially when I fly. Been sent to secondary immigration checks, secondary customs checks and even had my passport taken from me while they used it to compare to a 'suspect' passport that someone was using. They took so long with it I eventually reminded them that a UK passport was property of the UK govt and not Canada's and that they had no right to hold it for any longer than nessecary especially since I was not under suspicion and could I phone the British Embassy if it was going to take much longer. Basically I find Canadian Immigration a PITA.
Ive flown across the Atlantic 27 times (I had to count). Not once has UK immigration ever slowed me down. I simply walk thru the returning citizens line ( a seperate lineup for citizens, unlike in Canada, immigration takes about 30 seconds from the time you enter the hall to the time you pass the officer at Gatwick airport) and hold my passport open to my picture as the officer tells me "Welcome home sir"