Hello.
I’ve found the updated LR4 develop module to be a fantastic upgrade from LR3, and I use it if I have a small number of image files to process. I’m thrilled with the updated capabilities.
IF I have a large commercial job to run (200 to 1000+ files) that requires minimal adjustments where I can ignore the develop module, I revert to LR3. I’ve found LR4 to be virtually unusable running large jobs because it is so much slower than LR3.
My laptop’s hardware specs have even improved from months ago and yet the LR4 slowdown is dramatic. I am hoping Adobe updates soon to address this issue. Just Google “Lightroom 4 is slow”. The threads are prolific.