I always use the two hour rule. Most of the time I am early and have to just sit around. However, there have been a few times I've really needed that two hour cushion. This past Nov 26th, it was pouring down rain, so we were slowed down and then we ran into two separate bad wrecks where we were caught in traffic. I thought I was going to be late. On another flight this past year, I checked the departure gate just before leaving my house like I usually do, but then found that by the time I got to the airport a little over an hour away that they'd changed my terminal. Security was unusually long that morning and then I had to take the tram way over to the other terminal. Normally with the two hour rule, you'll be stuck sitting around the airport, but then again you never know what may happen between the time you leave home and get to your gate. I live a little over an hour away from my airport and always choose the first flight out, so I'm leavng my house about 2:30am every trip.