It honestly depends, this argument has been played out so many times (Slashdot, digg, reddit, etc.etc..) with the result of a stand still, depending on the scenario you use.

For example, you have the car analogy (seen above). You can have the property analogy (if my neighbor's wifi goes onto my land, is it then mine to use?). Then the whole issue of connecting is another issue. What if you have it setup to automatically connect to any open wifi? (Say your home is setup that way and you take your device roaming).

The courts would likely find in whoever owns the Wifi usually, but then again the court and laws themselves I rarely bother with (to easily are they bought in this day and age. I just follow what I believe is lawful and don't bother with what is unlawful and shouldn't be).