Hi Shark,
hmmm, I would not prefer this procedure. ALL images with ALL sizes should be derived from the original image in LR.
If you export images in LR to e.g. 2000px width (and also sharpen the images) and later on shrink the images from 2000px to e.g. 600px (and again sharpen them) then this procedure degrades image quality.
From my point of view all stuff should be handled in LR (or Aperture etc). This would be user friendly and ensures max image quality.
Manfred