Worried about your neighbor stealing your Wi-Fi signal? You could go the encryption route, or you could wait for the Wi-Fi blocking wallpaper to come to market:
French researchers have developed wallpaper that’s designed to trap Wi-Fi signals, without interfering with radio or cellphone signals. It uses conductive ink containing silver crystals to to block a Wi-Fi router’s operating frequencies: your router should work as expected, but the signal won’t travel beyond the wallpaper’s boundaries. While currently only a prototype, researchers at the Grenoble Institute of Technology hope to make the wallpaper commercially available early next year.
No word on how much it will cost, but I am guessing it won’t be cheap. The other downside? For full protection, you’d have to cover your ceiling with it as well.