In addition to what starbucks_mafia said (ie that the value returned by $ip and your IP as seen by others may be different), I'm not sure how you mean "everyone else sees $ip evaluating". Only you can see what your $ip evaluates to, nobody else. Others can see your IP by whoising you or otherwise, but they have no access to your $ip identifier (nor to any other identifier in your copy of mirc for that matter).
