The bbc has a story on the first criminal prosecution in the UK for using an unsecured wifi network.
This is quite scary, as I have used wifi networks i found to browse the net when bored. This is now an offence, and as windows automatically connects to wifi networks i may have even used them accidentally!
Of course you should always secure your wireless network, but now you cannot use one you find. What about free wifi networks? If I set up a wifi network in a public area, I would think about setting up open access with a restricted bandwidth so that anyone with a wifi pda or similar can use it. It costs me nothing, so why not allow others to get the internet on the move, but how do you tell if an open network is deliberate or not.