Many excellent comments and a couple of points not covered. I travel more for business than pleasure and stays average three nights. Although the housekeeper name placard is common, I have only rarely seen a "tips envelope." When I do leave a tip I always leave it in an envelope - usually from the hotel - and write either the maid's name on it or "housekeeping." This eliminates any confusion as to whether it was intended as a tip.

I am an easy guest, neat and clean, and usually inform housekeeping that I don't require daily service. If I do need an extra towel or toiletries I ask. One benefit of knowing the housekeeper's identity is I can greet her by name if I see her in the hallway, and thank her for preparing my room so well. That small gesture of respect and recognition might mean as much as or more than a two-dollar tip.

If the room was exceptionally spotless and well-organized upon arrival, I make a point of telling the GM and / or writing a brief note letting him or her know what a treasure they have employed.