We used a Debit one time (not at WDW) when we got the bill at check-out they charged us the wrong rate (too much!)..We questioned it and yes it was wrong, so they then charged us the correct amount.
The check out receipt showed the charge the credit and the new charge. What we didn't know is that the accounting office actually takes care of the "credit"...Well it was a Friday night of a holiday weekend, the accounting staff wasn't going to be in until Tuesday...So our Debit card was hit 2x for one stay....Luckily we were on our way home and had no plans to use the Debit card for any other purchases etc....
We now charge the room and pay it when we get home. I've also heard of hotels that "hold" $$. Example: if you have charging priviledges on your room key, they may hold extra to cover that...I'd hate to have money held on my "Debit" that I don't plan on using.