Tor is not invulnerable and using WiFi from random locations is recognized as a good technique for increasing your anonymity. Using WiFi from locations in a pattern can help a little, but if the feds want you and they know that you are going to connect to WiFi at one of a dozen locations the next time you use the internet for something and they can trace you, they will be able to get you if they try. If you use a neighbors WiFi it does give you the advantage of strong unlinkability if you quit using that access point and wireless adapter prior to the police getting to it, but it doesn't help a whole lot if you consistently use the same access point as wireless signals can be traced quite easily while they are being sent. I can't even recall a single case where the feds traced someone through the internet if they always connected from a new random access point and only kept online for brief periods of time. But again, there are several cases where they got people who fell into patterns of access points, and there are a lot of cases where they got people using neighbors WiFi. Another advantage of using hacked/open WiFi is that it hides the fact that YOU are using Tor (ie: it gives you membership concealment). This can be really good for security, particularly if you are a vendor, but again the level of protection it provides you depends strongly on how randomly you use access points and how long you use any given access point. You also need to worry that someone might notice you on their wireless network and call the police, I have not heard of someone identifying this through technical means but there are stories of people calling the police when someone in a car parks in front of their house while on their laptops. So you do need to be careful with not looking suspicious while using open/hacked WiFi networks.