It was supposed to be a transparent (forward)-effect for windows etc, but somehow turned into an opaque cube-mapped deferred shader...Not sure how that happened :)
Below you can see what the shader looks like at the moment, where the first two images show the 'forward' shader and the last two use the deferred shader (which includes pointlights, specularity etc.) The forward shader will be modified so it supports alpha-mapping, what it was originally designed for anyway.
|Forward shader - environment map, with normal map and simple directional light.|
|Forward shader - similar setup as above.|
|The deferred shader - with pointlight on the left and right (with very strong colors to highlight the effect)|
|Deferred shader - with the deferred rendertargets (LoR: color, normals,depth,lighting)|
The next step is to further develop the forward rendering pass, for transparency mostly. This includes depth-sorting of the objects along with Composite Lighting that calculates approximate lighting for objects that don't support deferred shading.
Custom Model Effect XNA Sample - Source for the cube-map processor and the basics for the environment mapping shader.
Shawn Hargraves on Cube-mapping - Some interesting bits about cube-mapping, closely tied to the XNA sample above.