Hey, a debian user requested (http://bugs.debian.org/614155) the ability to see window previews/icons in the window buttons plugins so I'm forwarding the request here. Regards,
I could add the icon, but that is bloat imho. The preview is something that window manager should implement (it should work with compiz), the panel only informs where the window button is located (for minimize effects, previews and things like that).
There's also a bug for xfwm4 which is #7318.