I fly 100 percent for leisure and usually alternate between making UA 1P (50K miles) and 1K (100K miles).

I used to do mileage runs until 9/11. I had about 50K in mileage runs that year and one of them found me stuck at O'Hare on 9/11. I stayed with good friends, but it was terribly difficult to be away from my family and made me do some thinking about pure mileage runs - those where you just fly back and forth.

As a result, I decided all my trips after those already booked would never be pure mileage runs. Now I usually fly with a friend or family member, to someplace I want to go and I stay at least a couple of nights. For me, this is not only healthier, but far more enjoyable.