I recently posted my experiences converting a large 3D Action RPG from Unity 3.5.7 to Unity 4.2.2. So if you’re an iOS developer thinking about making the leap from 3.5.7 to 4.2.2, you might find my post informative.
http://forum.unity3d.com/threads/208202-Unity-3-5-7-to-4-2-2-Upgrade-Experience-Report
Thanks excellent read and well written