A variation on your theme, I for the first time had a use for this--watching F1 practice sessions via the web and my screen saver kept kicking in. As I can't use Win32::API, I grabbed your code.

There were a couple of things that bugged me. I found the diamond pattern a little distracting. And if I used the mouse to adjust the volume or dismiss an email notification, the loop terminated and I had to switch away to restart it.

So I reduced the movement to a simple +1/-1 giggle at a reduced frequency and made it so that it wouldn't quit the loop until I moved the mouse to the top left corner.

#!/usr/bin/perl -w
use strict;

use Win32::GuiTest qw< GetCursorPos MouseMoveAbsPix >;

my( $x, $y )= GetCursorPos();
my $toggle = 1;
while( sleep 5 ) {
    my( $x1, $y1 )= GetCursorPos();
    exit unless $x1 or $y1;
    ( $x, $y ) = ( $x1, $y1 ), next
        unless $x == $x1 && $y == $y1;
    $x = $x1 + $toggle;
    $y = $y1 + $toggle;
    $toggle *= -1;
    MouseMoveAbsPix( $x, $y );
}
[download]