So if you've just installed or upgraded to the new version of Kubuntu (Wily Werewolf), you will notice that Skype runs fine but does not appear in the system tray as an icon. The workaround to fix this is to install the sni-qt package, but specifically the 32-bit version of the package (as Skype is a 32-bit app). To do this, open a terminal and type:
sudo apt-get install sni-qt:i386
This will also install a dependency. Once this is installed, quit Skype and restart it to find the familiar green check in your system tray.