Is there an attendant in the lounge?? If so, in North America you should probably tip.

For me this will vary depending on what my impact is... I frequent SPG properties much more often these days, and typically the lounge will do breakfast in the morning, and then some hot appetizers in the evening - seeing as someone has to refresh the food, clean up after me, wash my plate, etc... I think it is only fair that I tip them for this service.

If I'm only pouring my own coffee, or grabbing some bottled water, then I won't tip.

Also, this is assuming an attendant is present, if there is no attendant (honor bar) and the property has just left a collection plate out - you won't find me making any donations.