I can only tell you my own experience on this having agonised over your question for a long time myself (before learning about FT!) by the end of this year I will have flown nearly 40,000 miles on *A (since Nov 04) yet I'll have nearly 80,000miles banked - and that's without a FFP visa card. Plus the excellent miles + cash feature - which makes 'upgrades' across the *A very obtainable. BMI. If you actually want to use BMI regularly however.... that's a different matter. And as to how long BMI will stay in existence........