... with authors and license information like some other plugins/components do. The current "About" button opens the goodies web page.

Example code (by Olivier Duchateau):
http://code.google.com/p/xfce-ports/source/browse/misc/xfce4-weather-plugin/files/patch-panel-plugin__weather.c?name=4.10

Reference (xfce mailing list archive):
http://mail.xfce.org/pipermail/xfce/2012-September/031242.html