I was having problems getting my wireless to join my Ad Hoc network. When I would try to join I'd get an error, or it would look like it connected but with the wrong IP Address.

I tried rebooting the main computer supporting the network, didn't work. I tried manually typing the IP settings, kind of worked but only for a few seconds then it would drop connection and give me an "error connecting to network" message.

The solution I found was connecting my iPhone to a normal router, which solved the connection issues plus I had to manually set the IP settings. Now it stays connected.

The manually setting the IP settings I think has more to do with the computer I have running the Ad Hoc network, since I have to manually set DNS addresses on other computers on the network. Connecting to a normal router fixed the "error connecting" issues.