Yes only at the resort, but it is still worth it if you drink lots! Just got back from AKL and DH and I probably refilled our mugs 3-5 times a day. He had coffee in it some mornings, but mostly just soda and water. Its great considering one drink is usually $3. And it ends up being a souvenir!
Sadly, only at the resort. However, we LOVED our refillable mugs. We were on the dining plan and used snack credits for breakfast along with our free refills. And it was always nice to come back from a long day out playing and get our mugs refilled. They make a fabulous souvenir too. I still use mine all the time!