@andstatus Hm, is the /api/friendships/{show,exists,create,destroy}.format what you're looking for?

create/destroy take the locally stored ID of a profile as argument 'id' and creates or destroys a "friendship" (i.e. subscription, which sounds less brutal).
exists takes 'user_a' and 'user_b' as "subscriber" and "subscribed" respectively.

The locally stored ID should be available in the notices and updates, so for the home_timeline for example, it's the user->id property of a status.