I always build tips into my budget for the trip. I always tip a few dollars a day for housekeeping, and sometimes more. An example of excellent service encourages me to up the tip, and housekeeping is no different then table service at a restaurant.
A recent example is when we stayed at the AKL. As we were moving into our room, the housekeeper was a couple of rooms down. She stopped by and introduced herself (Maria, who has worked for Disney for 10 years) and said that she would be our mousekeeper for 3 of the next 4 days. She asked if we had any questions about the resort (my wife had a couple) and was very nice and very helpful. Animals did appear in our beds the next few days, and I tipped a little more than usual (5 dollars, 6, 7, and 8 on the last day). My kids looked for her to say goodbye on the last day (These are Teens and 20 year old kids, and for them to search out their mousekeeper was pretty impressive).
Did Maria's stopping by increase the tips? Sure. Did she ask or hint at tips? Not at all. Would the service have been as good without them? I never gave it a chance to find out, but the truth is that I never worry about that stuff. I have always tipped housekeepers at hotels and probably always will. A friend of mine who never tips the staff once told me that my leaving tips made it seem like everyone should, and that I was increasing the cost for everyone. He seemed irritated by the practice. I don't care. I work in the hospitality industry and believe in tipping the staff. I'm also the guy who doesn't care about the 18% auto tip on restaurant tabs (I increase it for great service, and complain to the manager about poor service). Again, I just figure 20% in when I budget for the meal. If I am worried about the budget (sometimes!) then we just eat at cheaper places.
My opinion? Tip the staff if you like the service. Housekeeping, baggage guys, waiters, etc. I always figure 10 bucks a day plus 20% on restaurant meals covers everybody if you stay at a nice hotel.
An interesting side note is that some upscale resorts now charge you for tips when you pay the bill. Disney doesn't do that, but I bet it will come to pass at some of their more expensive resorts. The last time I went to Hawaii, they added 20 bucks a day to the room charge, and it was itemized that way on the bill. They advised me about it when I booked, and it was on their website. When I inquired, they told me that it ensured that all the service staff received tips equally, and that it DID NOT include any restaurant tips. Hmmm.