I successfully installed OpenCV on Mac OS X 10.8.2.
After that I configured Xcode 4.5.2 by following this guide by SSteve even that this guide was for Xcode 3.5.1
Header Search Path: /usr/lib** (** stands for recursive search)
It's definitely wrong. You should setup this path like:
/usr/local/include/opencv2**
or:
/usr/include/opencv2**
From your link:
In the Search Paths section set Header Search Paths to /usr/local/include (/opt/local/include if you used MacPorts)