In my further test setups for class next week, I've been playing with wired/wireless configurations. What I've found is that by using Christian's utility, it isn't really necessary to use scripts for bringing down the wired interface. Interestingly, the wired NIC comes up first using DHCP, and then XWLAN brings up the WiFi card and enables DHCP for that. Both interfaces remain active. I haven't yet actually tested the individual connections (I was testing while docked, and never actually pulled the cable from the dock), but this seems infinitely easier than fussing with different scripts to bring the interfaces down and up.

Any thoughts along these lines?