To elaborate on that one: clown pass is cool, but not necessary anymore. Keyshot introduced renderlayers that everybody should start using. Put your stuff on render layers and render straight into a .psd. Keyshot will seperate every element PERFECTLY. Especially when rendering with dof the traditional clown layer approach quickly becomes a pain in the ass. It is a huge time saver especially when combining multiple renderings together, because now it is as simple as a drag and drop of a layer from one photoshop file to another.
While doing the dof in photoshop via depth map is an option to save a few hours I wouldn’t do it unless you really can’t invest the time. The difference in quality between photoshop dof and rendered dof is big and every trained eye can spot it because it has some very specific glitches.