Software
The Gumstix comes preloaded with Linux. However, it is unclear whether a GUI works with the Gumstix LCD interface in Linux. We decided to install Windows CE 5.0 on the Gumstix because there was hard evidence that the CE GUI works on the Gumstix. We can second that CE works with the LCD module on the Gumstix.
CE is also really great for quickly writing graphical apps once everything is up and running. Our E-book reader was written entirely in C# using Visual Studio (so we got Garbage Collection, a lot of data structures, and drawing routines for free). Also, it allows for convenient development on the desktop (much faster) using the .NET framework, with the porting step involving changing some function calls that are unsupported in the Compact Framework.
Installing Windows CE
We obtained the Windows CE board support package from the Drumstix Project, which includes detailed instructions about how to flash Windows onto the Gumstix. The binary-only build works well just to make sure everything runs, however, Platform Builder will be necessary when it comes time to set the correct configuration values for an LCD and to workaround the newer PBA31308 Bluetooth Module on the boards Gumstix is currently shipping.