I use XFCE and recently I have noticed that my Skype doesn’t show icons in popup menus. Perhaps that happened after emerge -uDNva @world 🙂 Search for a solution was not very long (https://bbs.archlinux.org/viewtopic.php?pid=940213): in my case, that was enough:
$ gconftool-2 --type boolean --set /desktop/gnome/interface/menus_have_icons true
Issue, restart Skype – and here are the icons.
For the great justice, one could also issue:
$ gconftool-2 --type boolean --set /desktop/gnome/interface/buttons_have_icons true