I too use them for vacations, and without them most of my vacations become unaffordable. I also find domestic coach tickets to be wonderful Xmas gifts. A little guilt sets in, that I didn't really pay anything for them (technically my employer did), but this passes quickly after I see how excited the recepient is.

I have visited around thirty countries (or foreign "territories"), mostly the courtesy of United Airlines over the last ten years. This has enriched my life, and I am forever grateful for frequent flyer programs, and my employer allowing me to retain the mileage.