"Something that does interest me, though, is that while we seem to see an increase in people asking for help about spam scripts, we don't seem to see the same increase in people asking for help with scripts that filter out spam - so maybe the situation isn't as bad as it seems."

I think the main reason for that is more people use Perl (or ASP or PHP) to automate outgoing mail in large quantities than for checking incoming mail.

The majority of people who use Perl to check mail do so using a web based client provided by a third party, which already has spam filters in place and has no option for users to edit the code.