Depends if I'm wearing a baseball cap or Kippah -- if the latter, got to tip every drink. If the former, you have more discretion.
SuperFlyer -- I'm a firm believer in tipping commensurate with the quality of the service -- but we're talking about the bartender in a lounge. How can the service vary so much in quality to make a difference??? They either gave you your beer or didn't
I suppose if they made you wait a while and seemed to keep doing other things....but I've never experienced that.