Lightroom 4's process version 2012 has a revised set of controls. For the most part, this will simply make your photos look better! Here's a brief explanation of some key differences, straight from Adobe.
Reshared post from +Jan Kabili
Lightroom 4 users – are you wondering why you don't have Fill Light and Recovery sliders in Lightroom 4? Here's the answer straight from Adobe.
http://blogs.adobe.com/lightroomjournal/2012/03/what-happened-to-fill-light-and-recovery.html
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Michael Preston
11 Mar 2012Well, at first, this old hack wannabe photographer didn't much care for the new controls…for the first half dozen or so images, I was almost screaming for the return of my recovery and fill light sliders. So I watched a couple tutorials by Matt K (of Kelby fame), and applied what I learned. For me, it turns out that the new process version is a godsend — my images look SO much better coming out of LR. Great job, Adobe.