It could be that your housekeeper gave you excellent service because she was just an excellent housekeeper. Or, as you said, that you tidied up yourself and didn't leave the place a mess for her.
Not just aimed at this poster, but as many have said, I'm sure the thing most appreciated is cash and leaving the room tidy for them. Plain and simple. As much as people spend all the time and effort making all the fancy envelopes and special ways of giving that cash, I'm willing to bet all that ends up in the trash before they leave your room. Not that they're ungrateful--it's purely an efficiency thing. Take the money out, slip it in a pocket, get rid of the rest of the "stuff". We tip every day, leave it in the envelope provided by Disney (or whatever hotel we're staying in), and leave it in on a conspicuous place. Our towels are all in one pile in the bathroom. There's nothing left on our beds. Our bathroom vanity area is kept tidy--we like it that way! And we've always had great service! No special treats, no handmade envelopes, nothing over the top.
I think the idea is a good-hearted one. But I think it's probably more for the giver's sake than the receiver's.