We are a Campaign Monitor customer, but we traditionally use the web interface. We're looking to implement a solution that would require use of the API, and that is a little beyond our skill set.
We have a custom website that sends a daily email to subscribers.
A cron job calls a PHP file that queries our list of active members (subscribers) and also retrieves the content of the email to be sent (also a PHP file). This is then emailed to the subscribers.
We would like to transition the process from PHP Mail to Campaign Monitor.
Please send contact info if you are interested.
Trone, my company, has done this successfully in the past and still uses it currently. You can reach me at firstname.lastname@example.org.