Patch attached. Need to call set_wireless_config, otherwise the device isn't actually set as ad-hoc, nor is the key or rate set to match the other node. And, of course, I use DHCP on my ad-hoc network. :) Perhaps it should check for dhcp, and then do autoip if that fails.
Created attachment 115322 [details] patch to make it work
Somewhat obsolete since we use wpa_supplicant now. However, there are a few issues still with Ad-Hoc, mainly that wpa_supplicant doesn't support setting the channel yet so "Create new Network..." doesn't work quite correctly.