I once heard that they sometimes throw all the little soap bars away, anyway, even if they're not opened. Don't know if it's true or not.
As for the maids. I've heard that down in Mexico, they expect a tip, and might do something cruel if they don't get one. The story I heard was that some maids once found somebody's camera when cleaning the room. They hadn't been leaving tips, so one took pictures while the others stuck the guests' toothbrushes up their own asses. The idea being the tourists don't find out their toothbrush has been up somebody's ass until after they get home and have the pictures developed.