AssFace,
I have been told that if you are going to throw away the values it is better not to even bother assigning the hash keys:

$hash{$thing}++;

versus

$hash{$thing} = undef;
[download]

I am not one for cargo cult programming. I honestly want to know why something is a better idiom for something than just doing it. With this said, I haven't thoroughly investigated this. I did do some benchmarks and the undef came out faster. Additionally, it makes sense that it isn't allocating any memory or doing any computation of the value.

Cheers - L~R