If I get a unexpected upgrade or some very special treatment by a gate agent or in the AC I always give them a book of Starbucks Coupons. I figure that they were simply kind to me and that NEEDS to be rewarded. If I pay for the upgrade then no coffee b/c I have not been given anything special.

I firmly believe that if someone goes beyond the job requirements for my behalf, then I owe them the recognition. It's simply good Karma.