Thanks for the heads up. I just checked and I have eight certificates that expire in June so I've PDF'd them and emailed them to my favourite employee in Bangkok so he can put a heart in the foam of my next breakfast cappuccino.
Unlike others on this thread, I do not consider it a great act of charity, compassion and gratitude to bestow these free certificates on employees because they cost me absolutely nothing and the giving is therefore an empty gesture and the employee knows it. I'm sure they'd prefer, you know, actual money as a appreciative gratuity if that's what the gift is intended to demonstrate.
If the employee is indeed "overworked, underpaid, underappreciated, taken for granted SPG employees" then a certificate got for free by the guest won't impress much (I'm sure there's some coupons in the local paper the can be cut out and handed over too) but a cash gratuity would be highly appreciated.