Last Friday I added support for metric into Route dialog. You can imagine metric as "preference" value.
Example of use:
We have 2 interfaces, eth0 and eth1. Both of them are connected into different networks with different routes (we have 2 possible gateways). Here we can set one of them as default gateway. When it somehow failed we lost connetion.
In situation above we can set both routes as a default route with different metrics. Set devices controled with ifplugd daemon. Route with higher metric is used as default. When device is disconnected, it's route is removed and the next one is used.
Current kernel doesn't use metric in static routing, Only routing daemons like multipathd does.