Wow, seems like there are a lot of people here who have more time on their hands during vacation than I do. I don't think I've ever watched to see if a person is using an old mug vs a new one. Heck the person in front of me can stick his head directly under the fountain and drink his fill and I would be so distracted by three kids clamoring for one more dole whip, one more ride on ToT or one more souvenir to notice. He could "steal" his fill, then take a mouthful back to his table and squirt it directly into the mouth of his daughter like a mother bird feeding her chick and I would be like "oh cool, my turn at the fountain finally".
Seriously, though, with the economic times like they are, I am thankful my DH and I can afford a trip back to WDW this year. We had to sacrifice and leave the kids at home *snickering* but we were able to manage it. If someone needs to save a buck by "stealing" soda, so be it. I bet it just means they HAD to take their kids with them