Matt, I think you misunderstood my question. I like doing blur post render (in comp). If it were available as a render option I would likely still do it in comp (unless the results were noticeably better.)
My point was many people look down their nose at using photoshop to do DOF blur when in fact their render engine is likely doing the same thing internally ->2d blur based on a z depth mask (Maya’s renderer as an example) Question is (was) do any renderers implement the DOF blur in 3D (like multi-frame) in a reasonable time or is it all basically done post render in 2d using a depth based blur mask.
Also I am unsure of the value of combining the depth and visible renderings in layers a single file. Would you chop the z depth to 8 bits (Ok for DOF blur but not a good idea if you are using it for z placement in a comp, particularly if objects intersect) or pad the 8 bit rendering to 16 bits (and double the size) or have a hybrid (8/16) that wouldn’t be compatible with image processing programs (PS, AE, ect) internal formats anyway. I like the flexibility of 2 separate files. It might be nice to have a checkbox in the render dialog for “also render z depth file”, so a rendering would render 2 files automatically.
What would be nice is to have the the option to separate the visible rendering layers (shadow, glow, reflections, ect) separated into layers in one file (as long as that file was an easy import into comping applications (AE, PS, Shake, ect…))