We had bought $800 worth of Disney Gift Cards from Sams Club before heading down (after hearing about it on here, of course) a couple of weeks ago and had no problems using them anywhere. My wife and I were a bit leery about them after reading a few posts on here of people having trouble getting them to scan in certain places down there, hence why we only bought $800 worth. But after being able to use them almost everywhere we tried, we bought another $600 worth at a nearby Sams Club off property while doing some shopping one day. We were using our room keys most of the time to pay for everything and then just going down to the front desk every couple of days and using the Gift Cards to pay off the room balance. Win - win really!!!!
The cool thing about them...they come in $100 denominations but only cost $98 and each $100 card comes with a $10 Disney Store card (which HAS to be used exclusively at a Disney Store, not the parks). We used them to buy some Disney towels and stuff pre-trip and just used the rest last week to buy some more cool Disney merchandise when we got home (like we needed it after just spending 10 wonderful days down in WDW)!!!