Living in an apartment, I found that many of my neighbors have not secured their wireless network. For example, one neighbor has a nice music collection.
I think this is a clear indication of how the computing environment is still too difficult for the average user. With that in mind, I recently ran across an article on Ars Technica, The ABCs of securing your wireless network, that helps explain the differences between the various networking options. The short answer is use WPA protocol to ensure adequate security.
For that matter, I recently threw away a wireless print server because it didn't support WPA. So, if you're running a wireless network, be sure to change the default password on your router and use WPA communication protocol.