"If you were walking down the street in a neighborhood and saw two houses, one had the front door and open windows (not the Microsoft type) and the other had a fence, bars on the windows and a locked front door; would it be legal for you to enter either house? No. "

I don't think this is quite the same. This is PUBLIC airwaves. If you are broadcasting out on public channels, with DHCP and no WEP, not only would it really be hard to make a case against someone just 'using' the network, but I would think the person could almost have as strong of a case going the other way saying "I was reverse hacked because your AP invaded my settings". An example of this:

A friend of mine installed a Linksys WAP11 and left everything default (SSID = linksys). One day he was browsing around onine and then went into the room where his AP and cable modem were. Funny thing is they were both turned off (and accident one of his kids did)!

A neighbor of his has the EXACT same setup (cable modem with WAP11) using all defaults. My friend had unknowingly been using the wrong network all day!