For about 50% of flights I have made (10 to 15 per year) I arrive the airport between 61 and 75 minutes before flight departure. So far I have never missed a flight but sure will happen someday. I have on many occasions in LHR been the last one to check in just as the 60 min mark has been clocked.

Personally I cannot see a reason to be in an airport any more than 2 hours before departure of a flight. For those wanting to get early so they can sit in a lounge and sip free drinks or snacks, do you not have chairs and drinks at home? Of course when I have time I stop by the lounge but would rather be home, work or elsewhere than hanging around in any part of an airport for hours.