I've been on in excess of 12 flights this year on Delta Air Lines. I was upgraded on all of these. Five of these upgrades were lucky because I was travelling stand-by on earlier flights - so I would have been glad to have just gotten on the plane ... Admittedly, I'm more likely to be upgraded because I fly on routes with frequent flights and widebodied planes like Atlanta --> Boston which has hourly flights and 767s and L1011s on a significant amount of flights!