As an affiliate I really dont mind Biz cards in the envelope, I just dont want a check or envelope that plainly reads descriptive text with dumb shit like "BIG PORN CHECK Dollars".
AS a program owner we issue all our checks reading only our corporate name and not my program name. Some affiliates might have to do some checking where the check has come from, but its much better than having a nosy mail man knowing your biz.
Epassporte also works well.