A little back story: One of our alpha user complained about this so much that we decided to delay our schedule to re-write CardMunch. We spent bulk of that time re-writing, and replicating the entire Apple address book framework.
What that enabled us to do is to create a completely separate address book from your personal address book. All of your business cards can go to either address books, and to switch between the two, it's just flip of a button. You won't have to worry about random business contact popping up in your personal address book.
I know it sounds a bit salesy, but the feature is really awesome. I'm glad we decided to implement it. I have about 800 contacts in my CardMunch address book for testing purposes, I would hate to put these in my personal address book.