You can set up a room charge with cash, travelers checks, Disney Dollars, a debit card or a credit card. They all work.
With credit and debit cards, no "hold" is placed on your account, and NOTHING is actually charged to your account until one of the following, whichever comes first: you reach the limit you set for the charge at check-in; you are near check-out time (usually the overnight hours of check-out day); or you call or request in-person that your card be charged.
Let me explain this last option .... Let's say you have a $1,000 room-charge limit, and you are currently at $995. If you try to buy something with your room card for $10, the charge will be declined. If you want to still use your room charge, you'd have to call the resort, and over the phone you can verbally authorize them to start another room charge for you. You'll then immediately be able to use your room charge again.
I got a print-out of my account a few times, so I knew when I was approaching my limit. When I knew I was within about $70 or so, I called the front desk, authorized my balance thus-far to be charged to my debit card, and then set up ANOTHER room charge account. WHatever I spent after that time was charged through as a separate charge on my debit card. So after my week at WDW I had only two charges on my debit card, about $725 for my first 6 days and about $60 for my last day.
Another tip about room charges -- you don't have to set up your room charge for the highest possible limit. At Value resorts, you can set up a room charge for up to $500, at Moderates it's $1,000 and at Deluxes it's $1,500.
When I stayed at POFQ a few weeks ago, when I checked in I set up my room charge for $800. I did the same thing last year at CBR. Both times, it was as smooth and as normal as can be. However, when I called the POFQ front desk before my last day during this recent trip to settle up my room charge and set up a new one (so I wouldn't have to have a charge declined and then have to take the time to set up a new one over the phone), the CM disagreed with me that I was even able to set up a room charge for under the $1,000 limit. I told her I'd already set up my existing one for $800, and she politely but firmly told me that was "impossible" because they "always automatically" set up the room charges for $1,000. I politely told her she was incorrect and asked her to check my account, and of course she found out the truth.