Ubuntu – Pidgin status icon in 13.04 / Raring Ringtail

Starting 13.04, applications will have to integrate into the indicators and can no longer have their own status icons in systray in Unity. (This may change in future.)

The Unity systray whitelist has been removed, so you can no longer whitelist applications to allow them to use the notification area in Ubuntu 13.04 Raring Ringtail. However, Java and Wine applications have been hard-coded as the only software still able to use the notification area so this change only affects some old applications that don't come with AppIndicator support. And since Qt applications systray icons are automatically converted to appindicators thanks to sni-qt, this change shouldn't affect too many applications.

Source: http://www.webupd8.org/2013/04/ubuntu-1304-raring-ringtail-final-beta.html