Interesting question. I just wrote about it on my blog last month.
CAUTION: link to my blog!
A Love Affair With United Airlines
From the feedback I received, it seems that many had similar stories.
Basically, I started flying on United when I was 9 and have never looked back. Family trips, mileage runs, and memorable trips around the world. When I went to law school, United got me home to LA every weekend. When I courted my wife, it was long distance via Germany. Every other month I was on a UA flight to Frankfurt. Oh what great memories that fostered long-term loyalty.