   d3d10 GS
  In d3d9, the POSITION element of a vertex must always be transformed to projection space after the vertex shader.  In d3d10, am I correct that this is not necessary if using a geometry shader?  That is, you can pass the unprojected vertices into the geometry shader, and then project them at the end of the geometry shader?Therefore, since clipping is done in projection space, clipping occurs after the geometry shader, but before the pixel shader???   
  Correct. If you use a GS it is responsible to output the transformed vertices.   