Tipping is definitely a personal preference, though guidelines and recommendations for tipping amounts exist. A recent article that I read stated that only 25%-30% of American hotel-stayers tip their housekeeping staff. (The article did not mention international statistics.) Granted that the housekeeper is not a front-of-the-house position nor one that solicits as much of your personal attention as a waiter or bellhop, still her efforts can have more of an effect on the comfort and cleanliness of your stay than just about any other's. And if she's doing her job right, it's not easy work. (My apologies to the male housekeepers out there. Most housekeepers I've seen tend to be female. Stereotyping hotel functions by gender, perhaps that's the subject for another poll.)
I was just curious to see what the overall tipping trend for housekeeping might be among a discerning group of more seasoned travelers.
Please feel free to add additional information as a comment in case the poll selections below don't quite match your housekeeping tipping habits.