I think you should keep register globals off because PHP highly reccomends it for security reasons. For instance, if you had chat board or something, and you logged people's ips, and you had 2 variables: $ip and $msg using POST, the person could still use the GET method for instance the user could fake their ip by doing
chat.php?ip=225.202.256.55&msg=Hi
if you used $POST that wouldn't happen. Thats why I try to avoid register_globals and $REQUEST[] as much as possible