A nice piece of guerilla marketing! Congratulations, Juerd!
It really is a well-known term in marketing and PR business:
Small companies can be very successful without ever spending a dime on an advertisement. When a group of Perl Mongers prepare for a YAPC or a Perl Workshop, they practise guerilla marketing: mailinglists, forums, usenet, PM meetings, targeted press releases, blogs, podcasts, Perl and programming websites, maybe even leaflets in internet cafe's or elsewhere, or posters at the local university or highschool. Low-cost, word-of-mouth, grass-roots.