Tough call. We stayed in high-end hotels that cost $200 a night. Yes, I know that's expensive for VN, but that level of accommodations would have cost double elsewhere. In the states, I tend to tip about 5% on the room cost, plus or minus depending. I personally think it would have been unkind to lower that rate simply because VN's average wage is lower. We left 2-3 $2-bills a day. We didn't do it in order to get better treatment, but I can tell you we certainly were treated better, from goodies left in our rooms, to explicit thank yous. That's where we used the $2s, for the housekeeping staff at the hotels we stayed at.

Different strokes, of course, but when we travel, trying not to "overtip" the people who clean our bathrooms isn't really a concern.