If I buy a house or move into an apt., I probably wouldn't secure my Wifi network. Getting a DS, PSP, Wii, + 360 to work with all that encryption bullshit is hard to do + DS and Wii are finiky about what passwords you can use. It's a lot easier to get everything to work if you just keep it open. Plus I kind of believe in keeping the Internet open for people.
If you just turn off your router at night when you go to bed or when you go to work, that should deter people from DLing kiddie porn and torrents on your account, right?