Any file that includes <QtGui> will produce this warning when compiled with GCC 4.8:

In file included from /usr/include/qt4/QtCore/QtCore:53:0,
from /usr/include/qt4/QtGui/QtGui:3,
[...]
/usr/include/qt4/QtCore/qtconcurrentfilter.h: In function 'QtConcurrent::ThreadEngineStarter<void> QtConcurrent::filterInternal(Sequence&, KeepFunctor, ReduceFunctor)':
/usr/include/qt4/QtCore/qtconcurrentfilter.h:108:47: warning: typedef 'Iterator' locally defined but not used [-Wunused-local-typedefs]
typedef typename Sequence::const_iterator Iterator;

The warning is harmless of course, but it's annoying because it repeats for every single file in my project, hiding the real problems.