Friday already! That was a quick week.
Great little tut. Very cool. I wonder about creating two stacked planes to simulate the actual width "in focus" region (DOF), but I guess that could get tricky because that also depends on cam distance from object.
Here is a scene file that will do about that with physical_lens_dof in MR
Same setup as before but with 2 planes the closer they get together the shallower the depth of field. Second plane controls in focus region first one focus depth.
Just took two small expressions and it's far from perfect, just a quick 2 mins to see if it was in any way feasible. If you want to play with it and fix the parenting and what not please do.
But here it is if you want to take a look at a version that will work with MR
Dave 
From a readers' Q and A column in TV GUIDE: "If we get involved in a nuclear war, would the electromagnetic pulses from exploding bombs damage my videotapes?"