Similar to kdelibs' bug #178322 ... 
 
Per fdo icon spec and http://fedoraproject.org/wiki/ScriptletSnippets (Gtk+  
Icon cache), something like the following should be added:  
  
%post  
for icon_theme in crystalsvg hicolor ; do  
  touch --no-create %{_datadir}/icons/${icon_theme} ||:  
  gtk-update-icon-cache -q %{_datadir}/icons/${icon_theme} 2> /dev/null ||:  
done  
update-desktop-database %{_datadir}/applications > /dev/null 2>&1 || :  
  
%postun  
for icon_theme in crystalsvg hicolor ; do  
  touch --no-create %{_datadir}/icons/${icon_theme} ||:  
  gtk-update-icon-cache -q %{_datadir}/icons/${icon_theme} 2> /dev/null ||:  
done  
  
Also wouldn't hurt to add  
update-desktop-database %{_datadir}/applications > /dev/null 2>&1 || :  
to both %post/%postun to register  apps that contain  
MimeType=  
in their .desktop files.