I was in the Admirals Club at MCI last week-the agents do bar duty and they absolutely refuse to accept tips.

As far as I know, at least wit US, the club bars are concessions, and as such, the bartenders are not airline employees. I have had this discussion with my favorite bartender at PHL and she told me that the club concession had just changed hands again-you can see an application for a liquor licence transfer at the club entrance.

So as I said before, I always tip--especially when the bartender is as nice as those in PHL.