Buying a wireless router for your home WiFi network, or having it sent to you free of charge by your ISP should guarantee a secure network.
Unfortunately, this is not the case and the list of default passwords for each brand of equipment is well known. If you have a wireless PC or laptop, you just need to look at the list of available networks in the area, and the type of encryption used. The first piece of information is giving you the manufacturer of the router. Few people know how to change the SSID from the default settings, never mind the authentication of the encryption on the network. This means that in a lot of cases, the wireless network can be access by anyone with little or no effort.
In most countries wardriving is legal( looking for open networks). What is illegal is to use the discovered network.
Why is the problem with open WiFi? You could be sharing the data on your computer, reveal your credential for internet banking (for example), and be legally liable for anything illegal taking place from your network .
When are manufacturers and ISPs going to start producing or supplying equipment that can either properly secure itself ? May be what is needed is equipment with a proper set of instructions usable by the general public.
NetSafe has been wardriving in the suburbs of Wellington, and the results are sobering. Have a look at this article describing the results.