Personally, I tip for good service irrespective of where I am in the U.S. (Polaris Lounge included) Tipping is the norm in the U.S. and I choose to recognize good service. I say "personally", because it is certainly a personal choice so I do it discretely as it is between me and the service provider. Outside of the U.S. tipping ranges from being OK to being a major insult to the service provider. I default to the local custom (a little research goes a long way) and act accordingly.