Add GNOME applets to the Xfce panel

Hmm, well, yes, I hear you: what for, why do that?
Just because ^^

1. Install xfce4-xfapplet-plugin from the universe repositories, then add it to the Xfce panel:

   

2. Choose a GNOME applet to add:

   

3. All done, the GNOME User Switcher is in place :)

   

Quoting the package description:

Description: Gnome applets plugin for Xfce panel
XfApplet is a plugin for the Xfce 4 panel. The plugin itself has no special functionality, its only purpose is to enable one to use Gnome applets inside the Xfce 4 panel just as they are used inside the Gnome panel.

Reference

Xfce Goodies Project