About your first part: I recently thought about a couple of app ideas that centered around integrating different web applications (facebook, dropbox, soundcloud

About your first part: I recently thought about a couple of app ideas that centered around integrating different web applications (facebook, dropbox, soundcloud, youtube). One of the red flags was what you described. The external service providers can pull the plug whenever they want. They can steal your idea, they can charge you for using their API. Of course, if you are lucky they might buy you, but I don't foresee too many 1 billion dollar acquisitions from Facebook in the future.