Flying Blue
Very important to me. I'm FB Platinum Elite for life, and I now avoid flying Air France KLM (or fly just enough to keep my miles valid). Why? Because in the past 5 years they have changed the program twice and reduced by half the value of my 2m miles (Europe to Asia used to be 120K return in business class, now over 200K-240K). If they had compensated a good customer, they would not have lost $100Ks of business.