Part of me said to leave this thread to die.  But here is one other factor one should take into account before putting on their gray hat and using someone else's WiFi....

Lets say you are using it to do some "other" security research and you don't bother to anonymize yourself.  Well now your neighbor's IP gets logged while you are "testing" a website or downloading some malware "samples."  Lets say that site was actually a government site and maybe not our government.  they intern start launching attacks on your neighbor and their system is compromised.  Next thing you know they are calling all their credit card companies and banks to file identity theft reports.  Or one more, someone uses their computer to hide child porn and some local law enforcement or fed track it down.  Lots of bad things happen because you felt that their "open" WiFi was an invitation for free internet. 

As ethical hackers, we have to look past the open doors and windows and take it upon ourselves to tell the owners to close them when we find them.  Regardless if there is a law to protect them or not.  I am sure a savvy lawyer could get such a case thrown out in court by stating "Well they didn't say NOT to use the open WiFi" and state that such signage wasn't present. 

Anyway just another way to think aside from the laws.

New York law is the most permissive.[1] The statute against unauthorized access only applies when the network "is equipped or programmed with any device or coding system, a function of which is to prevent the unauthorized use of said computer or computer system"

https://secure.wikimedia.org/wikipedia/en/wiki/Legality_of_piggybacking#United_States