Problem: Even though pastie is running it doesn't appear on Xfce panel's indicator-plugin. Well, this happens when the icon theme being used doesn't possess a "gtk-paste" icon. And that's what happens with the default Xubuntu 12.04 icon theme (elementary-xfce-dark).
Fortunately, all we need to do is borrow a "gtk-paste" icon from the "Humanity" themes (it comes installed by default in Xubuntu 12.04), and this icon will work well in dark and light panels.
Open a terminal window and run:
sudo ln -s /usr/share/icons/Humanity/actions/16/gtk-paste.svg /usr/share/icons/elementary-xfce/actions/16/gtk-paste.svg
sudo ln -s /usr/share/icons/Humanity/actions/48/gtk-paste.svg /usr/share/icons/elementary-xfce/actions/48/gtk-paste.svg
sudo ln -s /usr/share/icons/Humanity/actions/24/gtk-paste.svg /usr/share/icons/elementary-xfce/actions/24/gtk-paste.svg
sudo ln -s /usr/share/icons/Humanity/actions/22/gtk-paste.svg /usr/share/icons/elementary-xfce/actions/22/gtk-paste.svg
# Update icon cache for the elementary-xfce theme
sudo gtk-update-icon-cache -f /usr/share/icons/elementary-xfce
Note: You might have noticed I told that the default icon theme for Xubuntu 12.04 is "elementary-xfce-dark" and the above instructions are for "elementary-xfce", well the first inherits the latter, so we kill two birds with one stone.