NEWS in 1.2: Add ShoeBoxMaked.cs,, now you can export from Unity to ShoeBox. Only select a Texture with sprites and export.
This is a Importer from ShoeBox, a free Adobe Air based app for Windows and Mac OSX with game and ui related tools. I use it for make Atlas for my games. This script can import from ShoeBox to Unity and export form Unity to ShoeBox.
How to use: First in ShoeBox, before save you atlas, select default file format (.xml) and set "Tex Square" in true. Save.
Now in Unity the only file you need is "ShoeBoxReading.cs",it need be inside "Editor" folder. Now in Unity in Windows select ShoeBox Reading, and put the xml file, the texture that ShoeBox create, configure and done :D
Also there is a Editor Window that can help convert all sprite inside one Atlas to invidual prefabs.
Any problem, please ask.