I'm running OS X 10.8 and have Tunnelblick set up so I can connect to my OpenVPN server at home. I've also used this at $WORK in the past.
When I'm out and about and want to jump on a public network, I'd like to prevent any network traffic before the VPN is connected.
However, when connected to known "safe" networks, connections should be allowed without a VPN connection.
I think I can accomplish most of this with pre/post connect scripts in Tunnelblick, but that only works when the VPN connection is initiated. I need to hook in to the OS to have it automatically disable the blocks when connected to a whitelist of networks...