A friend pointed me to this excellent video that has the best explanation I have come across of the new process version in LR4 (PV2012). It really helped me to understand some of the very important changes that occur when using this new process version and why you will never want to do a bulk update.
Correction: I incorrectly posted the link to only Part 2.
Here are the links to both Part 1 and Part 2.
Part 1: Lightroom 4: The New Tone Controls
Part 2: Lightroom 4: Working With the New Process