It was accepted pretty much everywhere in the parks. Even outside vendors that are more permanent. Only place that didn't seem to accept it were carts that they roll around or balloons.
About a week ago we had no problem anywhere inside the parks... with one exception. The game card machines on the pier below screaming'/next to mania don't take them.
I have used Disney Gift Cards in Disneyland. And had no issues at all. I purchased everything from churros, to pretzels, and dinner at Blue Bayou, amongst other food and non-foodie fare.
There are a few merchants in the Disney park, that does not accept them, such as the crystal shop. Most DTD stores do not accept them, with exception of Disney owned business's, such as World of Disney.