I'm on OSX 10.5 with qt-mac-opensource-4.6.0.dmg from nokia's site. Qt Frameworks are in /Library/Frameworks
The strange thing is that the linker doesn't write the full path to the Qt Frameworks into the executable, like so:
otool -L ./Bitcoin-Qt.app/Contents/MacOS/Bitcoin-Qt
QtGui.framework/Versions/4/QtGui (compatibility version 4.6.0, current version 4.6.0)
QtCore.framework/Versions/4/QtCore (compatibility version 4.6.0, current version 4.6.0)
Note that there is no / in front of QtGui and QtCore.
macdeployqtplus apparently can't parse such a line and fails to deploy.
My suggestion would be to modify macdeployqtplus so that when encountering a path which starts with no "/" but with Qt*, macdeployqtplus prepends /Library/Frameworks.
Also macdeployqtplus can't find the plugins directory which by default is in /Developer/Applications/Qt/Plugins
Patches welcome: I don't have an OSX 10.5 machine to test a fix, but I can make sure that a fix that works on 10.5 doesn't break deployment using 10.6.
A patch for this was merged, so I assume this was solved. Closing.