I have David's compositing tutorial, but I was wondering if there was a way to render in layers not everything, but so that you could take the background, or the foreground, depending on what you want to focus on, and do some DOF softening effects in 2D in post? But still have shadows and such calculated? So I wouldn't need every light and shadow broken out, I'd just decide if I wanted to soften the background or sth. Like a 1-3 pixel Gaussian blur animated over time might look nice, keeping my subject in focus, and it would be a lot less render intensive.
PS. What I mean is, I would like to render out in layers that are kind of "grouped" I don't need every light and shadow, etc broken out. I would need to define the background, foreground, subject. Also I have to check the tutorial, but I would need to do the post effects in 2D in a Targa sequence, so I think that's just a matter of reloading the EXRs?