Here is my setup. ifplugd is managing the wired interface as eth0, and I have a wifi card using the airo module that is being managed manually and is eth1. If I bring up both interfaces, everything is fine, 'route' shows a default route for both interfaces. If I unplug the wired interface, ifplugd takes out the default route for both interfaces, and I obviously can no longer reach beyond the local network. Both default routes are restored when the wire is plugged back in. I have only eth0 specified in /etc/ifplugd/ifplugd.conf as the interface to manage.

I don't know if this is a configuration issue with ifplugd, an issue with how the network scripts operate, or something else, but on every other distro I have used, ifplugd only takes down the stuff associated with the managed interface, so there is something about Arch that causes this behavior.