I also give Starbucks coupons to ticket agents, gate people, and FAs when I receive nice service from them. This is AFTER the service has been received. I also attach a personal note or a "how well did we serve you" card with my MP number that they can turn into their supervisor that outlines exactly what I thought was so nice.

When I travel to Europe (France and Belgium specifically), I bring back chocolates and have given them to people at the CTOs who consistently provide me with great service. the last time I was upgraded from IAD-CDG by a gate agent at the last minute. I didn't have time at the time of boarding to thank her appropriately (since they were closing the doors), but when I came back through IAD I had a 2 hour layover and had them track her and made sure her husband (since she wasn't working that day) took them to her with a note from me. I don't do this expecting something from the person at all. They're given to say thank you for being nice to me.

I've done a lot of customer service in my career and there's nothing like a customer saying "thank you" to you when you've done something. Also, I don't believe you should give expecting something in return - not only is it tacky; it sort of defeats the purpose of giving, doesn't it?