In the standard Android WiFi doesn’t allow to connect to Ad-hoc networks. This might be out of security reasons, but when you are traveling it will save you money if you can connect to the WiFi on your laptop and use the internet connection in your hotel room.
There is a patch available from szym.
blackplatypus has done the patch. The file wpa_supplicant can be downloaded from XDA-Developers. (Credits to blackplatypus)
You have to exchange the file wpa_supplicant in your ROM or to flash the wpa_adhoc-signed.zip through recovery.