Many major headers are broken in the following way:
Take pango for instance.
Its headers are located in /usr/include/pango-1.0/pango.
There is no symlink for pango to /usr/include, #include <pango/foo.h> doesn't work while #include <pango-1.0/pango/foo.h> does.

Obviously, this cuses compile errors for many GUI applications, save the Qt ones.

In many of these libraries, /usr/lib/*-x.x/include/* isn't linked to /usr/include also.

I've observed this problem in the following libraries:
gtkmm
gtk
pango
pangomm
sigc++(1.0 and 2.0)
glade
gdk
gdkmm
glib
glibmm

The problem may be fixed by symlinking these libraries' inner directories and/or additional files, but _this may break things_.

A good way to find problem packages is to do:
[root@myhost include]# ls

...
libproblem-x.x
...

[root@myhost include]# cd libproblem-x.x && ls

Take note of the directories you see, then check for their existance in /usr/include.

Thanks for addressing this issue!