I used to, but I got too nervous about all the plaintext passwords and sensitive information that could be sniffed out of the air by a bored teenager. Enabling WPA isn't perfect, but it provides at least a single layer of protection which is probably good enough for most environments, similar to locking the door to your house.

My access point is wide open but SSID broadcast is disabled. Considering the number of visible open APs in my apartment building, that's probably enough to keep the random bandwidth leach or mischievous wardriver away.