Apparently, Ubuntu is getting rid of system tray in Unity… this affect all the applications (e.g. Skype) which have hardcoded system tray features. The old trick of whitelisting them does not work anymore, since the whole system tray is missing.

But there is still hope! In order to restore Skype tray icon in Ubuntu 14.04 it is necessary to install one single package:

$ sudo apt-get install sni-qt:i386

After reboot, Skype icon will reappear.

Original source: askubuntu.com