We stayed last September at the Vistana Villages time share property. They advertised "free shuttle to Disney theme parks". We had a rental van so we only needed to use the "free" shuttle on the fatefull day of September 11th when my DH left the kids and I to go to the parks alone while he drove a couple of hours north to take care of some business. We boarded the bus and saw that indeed, tips were expected. I was surprised, to say the least, being used to Disney transportation, which is truly free. I noticed that as each person left the shuttle they were putting a few dollars in and there I was riding with 6 of us to tip for (each way) . I did end up leaving a hefty tip, but was very glad that every other day we were driving a rental vehicle. I really left a nice tip on the way back when she evacuated us out of the parking lot after we were evacuated!
All this to say, if you are not saying on Disney property, you may feel pressured to pay for your "free" shuttle!!!