Using the web-based control panel, I can search all lists for a subscriber: http://help.campaignmonitor.com/topic.aspx?t=169
But I want to do this using the API. As far as I can see, the only option I have is this: http://www.campaignmonitor.com/api/subscribers/#getting_a_subscribers_details
Unfortunately, this will only search within a specified list. It won't search all lists.
Every time I want to look up a subscriber using their email address, am I going to have to search every one of my 100 or so lists?
It's actually just one API request you need to make to get all the lists to which an email address is subscribed.
Hope that helps!