Advanced e-Mail / customer automation?

Does anyone have any tips/advice on developing a more advanced email campaign manager?

For instance, it would be huge to get some custom rules, example;

After a purchase is registered in the system, one week AFTER the order has been marked shipped, the system will automatically send my customers a followup e-mail. This is a great way to keep your customers engaged even after a purchase, and will likely lead to return buyers or at least a great way to get feedback.

edit: Maybe I am blind, but is there any developer documentation around?