Comment 31 for bug 75358

Toward the problem of connecting an unsecured AdHoc Network (sg.openwireless.ch in my case) it's still in the 0.7.1 NM as delivered through the Network-Manager ppa for Hardy

But I was able to connect through wpa_supplicant to the network.

Here the wpa_supplicant.conf that made it possible, important was ap_scan=2 and mode=1
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ctrl_interface=/var/run/wpa_supplicant
eapol_version=1
ap_scan=2 #2 für Ad-Hoc Netzwerke wichtig!

 network={
 ssid="www.openwireless.ch"
 scan_ssid=1
 key_mgmt=NONE
 mode=1 #0 managed, 1 ad-hoc, 2 acces point
 }
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Since I use the madwifi-hal-0.10.5.6 I had to put the Card manually in AdHoc mode via
sudo modprobe -r ath_pci
sudo modprobe ath_pci autocreate=adhoc

The connecting via iwconfig was also possible, so it seems, that failure is in fact in NetworkManager.
(As a side note wicd had the same problem)