Even I'm having the same problem I can't edit a bridged connection nor can I edit Mobile Broadband Connection. I have seen this problem in various other distributions like Fedora. However, I have no troubles when connecting a bridged connection in Ubuntu 11.10. So this is something I guess that the GNOME maintainers forgot about
. Since most of the user base consists of direct-line connection ones which just have to be plugged into the LAN port and you're connected. I am also facing some issues with the driver of Broadcom 4311 which I guess I can resolve however the DSL thing is really annoying.