It's easy with one product, you have a non-buyers' list and a buyers' list. You promote your product to the non-buyers list, and to your buyer's list, you promote affiliate products.
But with two products, you have a non-buyers' list, and three more lists:
1. One for buyers of product #1,
2. another for buyers of product #2,
3. and yet another for buyers of both products.
It seems a lot of hassle, and just gets way more complicated with yet more products.
Anyone have any experience with this? How do you deal with it?