I was surveyed by United Airlines recently. They were happy with my travel for this year. Last year I flew 35K miles on them and I am just over 70k already this year. They were thanking me and asking what they can do etc... I told them. I think I surprised the woman as she kept coming back to "you are one of our most loyal customers" etc... I tried to explain, but don't think she ever got it, that I fly you because I have to not because I want to. My company gets good rates from you and you go where I need. As you can see from my recent post, I fly Virgin America whenever I can.
My two favorite airlines are Virgin America and Jet Blue. Unfortunatly they don't go international and they don't go, directly, where I need them to. I would rather be a bit uncomfortable (although now I am in upgrade a lot territory) than take an extra hop.
The loyalty program itself didn't do much for me until recently they added the ability to buy things. Now, using miles, I got a new GPS for the car for my wife and am getting a Wii. This is, I think, the best use of airmiles yet, as the last thing I really want to do is get on a plane for vacation.