SUMMARY: The rise of APIs as a source for web services and data means that developers don’t have to reinvent the wheel on every feature — they can source it from an API. This trend brings about the composable enterprise.
It is OK as long as you have an exit plan/alternative. If you know you can roll your own or switch to one of a number of providers in a week or so and that is a known risk you an can manage it.
Depending on what data you are trusting the APIs with there is also the security risk. CirleCI have just suffered from MongoHQ's security failure in a way that is extremely urgent and customer affecting.
http://gigaom.com/2013/10/12/armed-with-apis-developers-will...
SUMMARY: The rise of APIs as a source for web services and data means that developers don’t have to reinvent the wheel on every feature — they can source it from an API. This trend brings about the composable enterprise.