In my experience (admittedly very limited, i've only been 3 times) getting into the USA is easier than getting out again. I really don't like the biometric data they collect but at least once the system had it, re-entry was very quick. (less than 15 minutes gate to train at EWR which was pretty good from economy on a full TATL flight - even if it was a 767 not a 747, about 2 minutes at the immigration desk and walked straight through customs). Quicker than escaping from LHR on my return, why on earth can't they have a separate line for British citizens? I'd have made a quick exit from IAD too if my friends hadn't been held up for nearly an hour in the US citizen line.