The number of wireless networks around here is slowly growing, there was just one insecure network a couple of years ago. I just checked now, and I can find 6 other wireless networks, there's probably more during different times of the day.
The lower six networks shown here are all insecure. Three have no security what-so-ever, and the other three use WEP, which was part of the original 802.11 standard from back in the 90s and deprecated about 5 years ago as it can be broken in just a few minutes.
This isn't just about keeping people off your own network, this is about stopping people from receiving information you send back over the internet, when a machine is physically wired in, you'd have to be on a machine between you and the server to eavesdrop - on a wireless network however information you send out goes to everybody around you as well. A lot of non-financial information is still sent over the internet as plain text, use a lot of social networking sites? Your password gets broadcasted as plain text, if your network isn't secure anybody can get your password and username, the same goes for web forums, a lot of e-mail servers etc.
Make sure your wireless networks are set to use WPA or higher, pretty much all devices nowadays support WPA (the Nintendo DS is the only exception I can think of - I have no idea why Nintendo don't do something about this).
If there are legitimate reasons for why a network needs to be open, make sure you use HTTPS when available, even if the server doesn't have a certificate to prove its identity.
Manufacturers should also do their part and ensure WPA or WPA2 are the default options. All WEP does is provide a false sense of security, the fact it is deprecated and insecure should be made clear when the user is configuring the device.