Foregoing lamenting my own slacking, I want to point everyone who cares to read this to a great online resource I stumbled upon today:

A free online book called "Programming Vertex, Geometry, and Pixel shaders"

It is geared towards D3D10, but it contains an incredible wealth of information about nearly every graphics topic you'd want to implement. The concise and thorough theory certainly holds for XNA and most shaders should give you a good idea how stuff gets implemented, if they don't work out of the box. It's written by these guys, who deserve a truckload of cookies in my opinion!

_{Oh and Jack, if you ever should find your way here, we have to discuss your definition of 'not very active' :)}