NetworkManager updates seem to do a very poor job of maintaining compatibility with configuration saved by earlier versions of NetworkManager. I don't know if it is lack of sane schema migration or something else, but when (after updating the NetworkManager stack) networking goes flaky, I sometimes have to do the following steps to return my system to having working networking.

$ killall nm-applet
$ sudo service NetworkManager stop
$ gconftool-2 --recursive-unset /system/networking
$ sudo service NetworkManager start
$ nm-applet&

Of course, this removes all my networking configuration, so I have to start over. But that's better than totally broken (or just flaky) networking.

It is very annoying when the system that requires this action belongs to a less Linux-savvy family member whose networking has just been damaged by an update to NetworkManager.

I sure hope that as NetworkManager moves to being the core network configuration tool for systems, it gets more reliable! As it is, I feel that NetworkManager has been earning the epithet "NetworkMangler" that I've heard applied to it so often.