Link to September 30 tech.yahoo.com post, "Anti-Wi-Fi paint keeps your wireless signal to yourself".
Excerpt: The idea is simple: Use a special paint on walls where you don't want wireless to pass through (say the exterior of your house). The secret is mixing aluminum-iron oxide particles in with the paint. The metal particles resonate at the same frequency as Wi-Fi and other radio waves, so signals can't pass through the thin layer of pigment. Outsiders would simply be unable to access your wireless network, just as you, inside the house, won't be able to interlope on anything beamed on the outside.