How make changing to the /etc/hosts file take effect?
The Cisco AnyConnect VPN Client is known to show this behavior. It will reset your /etc/hosts file on reboot to the contents of /etc/hosts.ac.

If you use this VPN client, you should make your modifications to both files.

See this hint for more info.

http://hints.macworld.com/article.php?story=20111011050950471