Use of standard status icons in Empathy
One of our goal for Empathy 2.31 is to use standard status icons rather than empathy specific ones. That means Empathy will respect the XDG Icon Naming spec so icon themes will be able to easily define their own icons.
Currently some themes, such as Ubuntu's humanity icon theme, already define their own status icons by implementing empathy-* icons. If you are a theme author be aware that this won't work with Empathy 2.31.x so you'd probably want to implement the official icons as well to ensure that your theme will continue to work properly with future releases of Empathy. That's what the humanity theme has done for example.
Note that the user-invisible icon isn't officially part of the spec but Empathy will make use of it. I requested to add it so it should hopefully be integrated at some point.
I also sent an email requesting to rename user-idle to user-extended-away as the current naming is pretty poor but until it's accepted you should continue to use the current name.
Empathy using Ubuntu Lucid's icon theme