My position on this is that if the access point is open then it may be freely used. There are an increasingly common number of free hot-spots over the UK. Imagine if you were using Bristol wireless but moved too close to a Wurzel's unsecured home network. You'd be breaking the law through no fault of your own. It's about time people took responsibility - if a network point is open - it's free for anyone to use. If you don't like it - then secure it.
What do people in the know think? (I'm guessing my readership would have some good opinions on this.)