If you wait long enough, someone will build an interactive front-end for anything. DrJava, for example, comes with a little interpreter that lets users type in simple expressions to explore the state of their code, while the people building the software for the particle detectors in the next-generation collider at CERN use a C++ interpreter.
And now this: interactive browser-based front ends to a variety of web APIs, including Flickr, FaceBook, and Amazon. Type it in, click the button, and see what happens --- it's a great way to hear yourself think. If either of the Eclipse projects we've put forward for the Summer of Code is accepted, we're going to need to build some web APIs; a testbed like this would be a great accompaniment.