Yes, I am developing with Xcode 4.5.2 on OSX 10.8 setting deployment target to 10.6. The deployed version works only on 10.8, but if I do the same on 10.7, it works fine on 10.6-10.8.

I believe it depends on what kind of functionality you are using in the project. Perhaps, your project doesn't need CoreText.framework or ImageIO.framework. My hardest issue is about missing symbols in system libraries, that doesn't seem to be actually related to macdeployqt as long as it sets only library paths.