The main problem with Blender is that unlike all other renderers that I am aware of it does not have the ability to import vertex normals along with polygonal data, which is a big problem when trying to render CAD data.

See here for some previous discussions on this:

http://moi3d.com/forum/index.php?webtag=MOI&msg=5083.6
http://moi3d.com/forum/index.php?webtag=MOI&msg=4515.3
http://moi3d.com/forum/index.php?webtag=MOI&msg=4272.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=4409.79

-Michael