What us the API Key field used for?

Within the settings screen within for the app there looks like there is a unique API Key that is associated with my account. All I can find in the forum is a suggestion to expose an API from a couple of years ago. Has the web API been stabilized to the point where you would be comfortable with external developers using the API? If so is there could someone upload any documentation to the forum for us programmers?

Jason Turan