UPDATE (6/14/09): The Wegmans markets in Downingtown and Warrington, Pennsylvania and Mt. Laurel, New Jersey are carrying the mixes.
I just returned from Wegmans in Cherry Hill, New Jersey, where all four Betty Crocker gluten-free dessert mixes are on the shelf. The brownie, chocolate chip cookie, yellow cake and devil's food cake mixes can be found in the baking goods aisle, not in the market's "gluten free" section. The mixes are made with a rice flour and potato starch base, along with other ingredients depending on the variety. The brownie and cookie mixes contain soy ingredients, while the cake mix labels state that those products "may contain soy." The mixes are priced at $3.99 each.
The company's website offers "no butter" instructions that call for the use of vegetable oil or shortening to replace the butter suggested on the products' packaging.
General Mills tells me that the products' roll-out started on June 1, and that most supermarkets should start carrying the mixes by July 1. If any readers have found them at other markets, leave a comment to let others know about it.