In fact in many cases it is now standard procedure for law enforcement to check if someone is having their wifi stolen prior to raiding them http://www.geek.com/articles/chips/wireless-router-exposes-child-predators-using-the-internet-20090615/ here this details one device they use: http://www.pcworld.com/article/238107/cops_use_device_to_find_child_porn_on_wireless_networks.html It used to be they would always raid the person whose IP address showed up in their investigations, but now they are more patient and will analyze wireless connections prior to determining who to raid. So no, using neighbors wifi is not very helpful. It is better than not, but only very slightly.