The team over at Security by Default wrote up a nice blog post about Firewall Builder recently. Here's a link to the original article which is in Spanish:
And, if like me you can't read Spanish, here's a link to a translated version in English. It's not perfect, but the key messages come across.
http://bit.ly/pAu1hF (English translation via Babel Fish)
Always great to hear about how people use Firewall Builder and what they like about it!