The difference between LR3 and LR4 is significant, and I'm currently reviewing and reworking many images.
The Adjustment Brush has been especially useful for cleaning up backgrounds of closeup flower shots.
I use the Adjustment Brush (K key) with: No feathered brush, Contrast -100, Shadows +100, Sharpness -49 (no more), Noise +100, then I trace around the object I want to remain in sharp focus, and with the above settings, the bg becomes more softly blurred and out of focus (it will alleviate some poor bokeh). Using the space bar temporarily disables the brush so one can mouse around the image (I usually work at 1:1 or 1:2).
By setting Exposure to -100, the bg can be made black (may take more than one pass), and of course the WB, etc. can be changed also.
With the added power of LR4 over previous editions, I have touched PSE for well over a year, and there seems to be less and less need for anything else (I'm able to avoid major surgery with more thinking in the field).
Glenn
As shot - using a black cloth background (which wasn't completely black):
Reworked using the Adjustment Brush:
