When no VPN plugins are installed and you run nm-connection-editor and click "Add" button to add a new connection, the editor crashes with error: "Unknown type NMVpnPluginUiInterface specified in treemodel new_connection_combo_model" The workaround is to install a VPN plugin.
network-manager-applet-0.9.7.0-3.git20121016.fc18 has been submitted as an update for Fedora 18. https://admin.fedoraproject.org/updates/network-manager-applet-0.9.7.0-3.git20121016.fc18
Jirka says an automatic connection to wifi network works on LiveCD, but you can't set it manually. Might be a final blocker.
Package network-manager-applet-0.9.7.0-3.git20121016.fc18: * should fix your issue, * was pushed to the Fedora 18 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing network-manager-applet-0.9.7.0-3.git20121016.fc18' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2012-16227/network-manager-applet-0.9.7.0-3.git20121016.fc18 then log in and leave karma (feedback).
The update was pushed stable, and I just tested in Beta RC1, cannot reproduce - booting live desktop, running nm-connection-editor and clicking Add works fine. Closing.