I'm responsible for keeping Spam under control at Manux Solutions.
I am happy to post any custom rules that I use to tag our spam specifically.
What I'm not too happy about is the documentation for SpamAssassin.. So I will be helping out the Wiki where I can. I think there are a lot of things that people don't learn, and probably don't get the chance to, without being avid linux users for some years.
Manux Solutions Limited http://www.manux.co.nz/