I have also heard to change your WEP (20 character encryption code) bi-weekly. Depending on the level of usage, a kiddie with a sniffer could get your code in 3-4 weeks. If you keep changing, he will give up.
BTW, you have to look at your surroundings. My neighborhood has 1 acre lots, and shiatloads of blue hairs. My buddy on the other hand set up his wifi, and had 6 other people broadcasting available networks.
Needless to say, he put his up in a very secure fashion.