My experience has been with no checked bags and a pre-printed boarding pass you are fine with a one hour check in. If I am going to check a bag I would be there at least 1 3/4 to 2 hours ahead. With a larger group and multiple checked bags I would look to be closer to the 3 hour suggestion. Lastly, I would say things have gotten faster since you no longer have to complete the "blue card" customs cards. All of this assumes you are a visa exempt traveler into the US.