I used Global Entry for the first time today at IAH and it was so painless and so quick. As others have noted, there was a CBP officer there to assist at the kiosk.

As you would expect, I did receive some stares when I skipped the US citizen immigration line to go to the kiosks. When I got to customs, the officers pointed out the Global Entry lines on the far left and right sides and told me to be sure to take them in the future so as to speed my way out. We discussed the fact that the sight of some travelers skipping immigration lines and going to the head of customs lines was about the best advertising for the program. One CBP agent at customs said, 'Well, you paid for the privilege."

There appeared to be only about one plane's worth of passengers in the US immigration line today at 5:30 am when I arrived at immigration. When the surge hits out of South America later in the morning and out of Europe, Central America and Mexico in the afternoon, the GE registration process would have to seem even more worthwhile.