In a CGI if you do:

die "Bugger!\n";
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then the user will not get an error message. Typically they will get a 500 internal server error or a blank screen, depending on if a header has been output. They will not see the error message. A die nice routine might be:

# sack the QA team! 
sub die_nice {
    my ( $real_error ) = @_;
    email( $ADMIN, $real error );
    warn $real_error;                 # this will log it like die
    # Make sure we have a valid header....
    print "Content-Type: text/html\n\n";
    # Lie to the user, we don't want to let them know our code is unst
+able now do we?
    print "
<p>Sorry the server is unable to respond to your request due to routin
+e maintenance
<p>Please try again later....";   # yeah right.....
  exit 1;
}
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So rather than die-ing you die nice ie do some stuff you want. You could just set a DIE handler but.....