Dropbox Automator lets you automate tasks on your Dropbox account
APIs are awesome and services like Dropbox Automator shows the capabilities of online APIs.
Dropbox Automator is aimed specifically at the users of Dropbox. It enables you to set automated actions that is performed on files stored on your account as they are added.
You can for example set it to upload photos to your Facebook account or process documents. Here is a snapshot of the list of actions available right now: