I'm having a weird problem with FXC and DirectX 11. Running on a DirectX 10.0 compliant (admittedly crappy) integrated graphic card, my shaders are not working if I use FXC to compile them at build time with the flag /Od. Looking at the graphics debugger in VS 2012, I see the input assembler and vertex shader stages of the graphics pipeline correctly, but the pixel shader stage is missing, so the geometry is never drawn to the framebuffer, like so: 
Using /O0 works, but then I lose the ability to debug shaders effectively (optimizations, even at /O0, seem to scramble the instructions, so they don't match the .fx source file)
On another machine, with a DirectX 11 card (GTX 560), /Od works fine.