Same here. I have been attempting the in Feisty, Gutsy and now Hardy without success. 

Attached is the relevant messages log from Network Manager.

In short, the important messages are:
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Creating network 'motin-laptop' on device '/org/freedesktop/NetworkManager/Devices/wlan0'. 
Jun 28 17:59:01 motin-laptop dhcdbd: message_handler: message handler not found under /com/redhat/dhcp/wlan0 for sub-path wlan0.dbus.get.reason
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Device wlan0 activation scheduled... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) started... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) scheduled... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) started... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) scheduled... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) complete. 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) starting... 
Jun 28 17:59:01 motin-laptop NetworkManager: <info>  Activation (wlan0/wireless): access point 'motin-laptop' is unencrypted, no key needed. 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  retry to connect to global supplicant socket (try=1) 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'INTERFACE_ADD wlan0^I^Iwext^I/var/run/wpa_supplicant0^I' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'AP_SCAN 2' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'ADD_NETWORK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was '0' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'SET_NETWORK 0 ssid 6d6f74696e2d6c6170746f70' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'SET_NETWORK 0 mode 1' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'SET_NETWORK 0 frequency 2412' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'SET_NETWORK 0 key_mgmt NONE' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: sending command 'ENABLE_NETWORK 0' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  SUP: response was 'OK' 
Jun 28 17:59:03 motin-laptop NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) complete.

Followed by repeated:
Jun 28 18:00:20 motin-laptop kernel: [11976.775999] wlan0: Initial auth_alg=0
Jun 28 18:00:20 motin-laptop kernel: [11976.776011] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:21 motin-laptop kernel: [11976.909591] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:21 motin-laptop kernel: [11977.026622] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:21 motin-laptop kernel: [11977.141840] wlan0: authentication with AP 00:00:00:00:00:00 timed out
Jun 28 18:00:23 motin-laptop kernel: [11978.661601] wlan0: Initial auth_alg=0
Jun 28 18:00:23 motin-laptop kernel: [11978.661606] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:23 motin-laptop kernel: [11978.836640] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:24 motin-laptop kernel: [11979.026279] wlan0: authenticate with AP 00:00:00:00:00:00
Jun 28 18:00:24 motin-laptop kernel: [11979.226240] wlan0: authentication with AP 00:00:00:00:00:00 timed out
Jun 28 18:00:25 motin-laptop NetworkManager: <info>  Old device 'wlan0' activating, won't change. 

Ending in:
Jun 28 18:01:03 motin-laptop NetworkManager: <info>  Activation (wlan0/wireless): association took too long (>120s), failing activation. 
Jun 28 18:01:03 motin-laptop NetworkManager: <info>  Activation (wlan0) failure scheduled... 
Jun 28 18:01:03 motin-laptop NetworkManager: <info>  Activation (wlan0) failed for access point (motin-laptop) 
Jun 28 18:01:03 motin-laptop NetworkManager: <info>  Activation (wlan0) failed. 
Jun 28 18:01:03 motin-laptop NetworkManager: <info>  Deactivating device wlan0. 

It is clearly not setting up a correct Ad-Hoc AP, since 00:00:00:00:00:00 definitely looks like an invalid address...

Note about hardware: On my old laptop using ipw2200 (on which I haven't watched the messages log during an attempt), it could be related to the hardware (Bug #75358). This time, it is however a clean install of Hardy on an XPS M1330 using the Santa Rosa Intel Wireless Chipset (unsure of which one it is but someone mentioned chipset Intel 4965 AGN on http://ubuntuforums.org/showthread.php?t=743660).