I'm using Ubuntu 12.10 with Gnome 3.6 on a brand-new Samsung NP900X4C.

The installer detected the wireless adapter, took in the SSID and WPA passphrase, wrote these into /etc/network/interfaces and connected perfectly.

Once installation was finished I wanted to switch to using NetworkManager to manage the wireless adapter, since this is much more convenient than fiddling with /etc/network/interfaces every time I find a new hotspot.

Therefore I edited /etc/NetworkManager/NetworkManager.conf to set:

[ifupdown]
managed=true

When I rebooted NetworkManager, the problems started: - The NetworkManager tray applet changed from saying device not managed to device not ready - I lost all internet connectivity as wlan0 would not associate to the Access Point - if I set managed=false in NetworkManager.conf and restarted both NetworkManager and networking services from the command-line, the Gnome desktop "semi-crashed" and lost all its Window Decorations, the panel, the launcher and basically became unusable.

However if I restart the computer completely after setting managed=false, wlan0 once again works perfectly.