You will find in a few lounges, the attendant becomes fawning and borderline obsequieous (The Boca Renaissance, Omaha Marriott and Norwalk Marriott come to mind). Usually those people are fishing for a tip.

If the attendant has genuinely been of some help beyond the normal attendant's duties (i.e. as a concierge), I will tip. Otherwise, I treat the lounge as self-service.