I just read an old thread, not answered.
I discovered strange behavior of the XFCE panel. When loading Skype (autostart at login) the icon is partially hidden under other panel items or lost at all. Restarting Skype helps, as well as resizing the xfce4-panel (and putting it back to original size)
I know that this is not an important problem, it is purely aesthetic problem, but still, it is a problem.
I guess that i could solve it with changing the skype tray icon, but, i can not seem to find it anywhere....