why can't I use regular class libraries in XBox360 games?
I have application logic which I want to keep independent from XNA and use in both WPF and XNA applications.
Does anyone know good practice to share code between XBox/Phone7 applications and "regular" windows applications?
Have a look at Portable Class Libraries: http://msdn.microsoft.com/en-us/library/gg597391.aspx
Using the Portable Class Library project, you can build portable assemblies that work without modification on the .NET Framework, Silverlight, Windows Phone 7, or XNA (Xbox) platforms. Without the Portable Class Library project, you must target a single platform and then manually rework the class library for other platforms. The Portable Class Library project supports a subset of assemblies from these platforms, and provides a Visual Studio template that makes it possible to build assemblies that run without modification on these platforms.