Using a neighbors wifi is probably not very helpful for anonymity but the chances of being raided or even talked to by police for it are extremely remote. There are very very very very few cases of people being bothered for stealing wifi and in all of the cases I have found they were working on a laptop while parked in front of the house that they were taking wifi from. Not many people have the technical skill to determine that someone unauthorized is using their wifi, even though it is often as simple as checking the routers interface and seeing the MAC address of all connected devices. Even the people who know what a MAC address is and know how to check logs from their router are not likely to do so unless they notice their internet is going slow as shit. People with open wifi or WEP are even less likely to know how to detect people stealing their wifi, if they knew this much they would probably know to not use WEP in the first place. Even if the person who owns the wifi AP you are using does determine that someone unauthorized is using their internet, they will not be able to determine who is doing it unless they know how to trace a wireless signal. If they call the police over it they might know how to trace it back to you though, so in theory you could get in shit for it. This never happens though.