Icon Cache
If an application installs icons into one of the subdirectories in %{_datadir}/icons/ (such as hicolor in the following examples), gtk-update-icon-cache should be run after the package is installed/uninstalled on FC4 and later. This is required so that the installed icons show up in GNOME menus right after package installation, and speeds up GTK+ applications' access to the icons. For KDE, just 'touch'ing the top-level icon directory is enough.
Note that no dependencies should be added for this. If gtk-update-icon-cache is not available, there's nothing that would be needing the cache update. Not adding the dependency on gtk-update-icon-cache (ie. gtk2 >= 2.6.0) makes it easier to use the package (or the same specfile) on systems where it's not available nor needed, such as older distro versions or (very) trimmed down installations.
%post
touch --no-create %{_datadir}/icons/hicolor &>/dev/null || :
%postun
if [ $1 -eq 0 ] ; then
touch --no-create %{_datadir}/icons/hicolor &>/dev/null
gtk-update-icon-cache %{_datadir}/icons/hicolor &>/dev/null || :
fi
%posttrans
gtk-update-icon-cache %{_datadir}/icons/hicolor &>/dev/null || :