How can I get the Skype notification back in the system tray?

Solution 1:

You can get skype tray in 11.10 and 12.04 installing package sni-qt:i386

sudo apt-get install sni-qt:i386

OR

You can whitelist systray as well

How do I access and enable more icons to be in the system tray?

OR

If you like how empathy and messaging tray work you can install a third party skype-wrapper package from ppa which enables Skype to indicator-message

You can install it with

sudo add-apt-repository ppa:skype-wrapper/ppa
sudo apt-get update && sudo apt-get install skype-wrapper

SOURCE

Solution 2:

Install dconf-tools / sudo apt-get install dconf-tools.

Then run the conf editor by typing:

dconf-editor

at the command line.

There under Desktop > Unity > Panel

change the line that says:

['JavaEmbeddedFrame', 'Mumble', 'Wine', 'hp-systray', 'scp-dbus-service']` 

into this here:

['JavaEmbeddedFrame', 'Mumble', 'Wine', 'hp-systray', 'scp-dbus-service', 'Skype']

You can change it to ['all'] which allows all tray applications to show there icons in the indicator bar (Ah-Duh!). As usual changes will take effect only after reboot or restarting unity by Alt+F2ing

unity --replace &