At any rate, that can't happen with my wi-fi, as I have wireless security turned on, and I've also changed the default password (which quite a few people forget to do). Today's case was in Britain, in west London to be exact, but it's happened in the United States as well.
In Britain, it's a crime. Fraudulently obtaining free internet access falls under the Communications Act 2003 and it's also a potential breach of the Computer Misuse Act. I'm not sure about the United States, but it's certainly not ethical, and readily preventable.
The unidentified 39-year-old man was arrested after he was noticed sitting outside a house with his laptop, and later posted bail.
Despite the fact that it's a crime, the screw-up here is that there was no security enabled on the wi-fi router. It's not that hard (OK, maybe it would be too hard for my mother-in-law), but even if it is there are tons of resources out there on the web on how to enable security - although the difficult part for some would likely be that the interface for controlling the router will be different from manufacturer to manufacturer, and often, from model to model within the same manufacturer.
Still, it's not that hard - and if your wi-fi signal is unprotected someone diligent enough could latch onto some sensitive data from your network - if he tried hard enough, anyway. So get with it folks! Enable your wi-fi security!