Another thing is that if they gave you the miles when you buy the ticket, that ticket might be exchanged for a different one at a different price and distance. Personally, I'd like to see them give miles for revenue spent (maybe something like 5 miles per dollar?) And as I stated before, some airlines are heading roughly in that direction anyway.

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United UGS, 1K, Million Mile Flyer
Hyatt Lifetime Diamond
Starwood Platimun