I was on a transcon recently, where nearly all the F pax were making many requests, along with several special requests. The two FA's who were staffing F were really hustling to serve the meals and meet all the drink requests. A third FA from Y was needed for a short time. When one of the FA's came by with a nearly empty bottle of wine, I remarked, "Wow, you all are really hopping tonight." The FA was very gracious and thanked me for noticing. I remarked to the FA that they were handling it with a lot of poise. Later I had a nice chat with the FA's and they expressed sincere appreciation that I had noticed their hard work. I guess my point is that sometimes less is more, and just a verbal acknowledgement, delivered genuinely, is the most appropriate gesture.