My personal favourite is manipulating $0.

At random parts in my program where the state, according to the OS, is running (whcih is correct), I like to tell what it's doing to the layman at work.

my $origName = $0;
...
$0 = "$origName: Processing file $n.";
...
$0 = "$origName: Sleeping for $y seconds.";
...
$0 = "$origName: Eating some cheese.";
[download]