I activated my Flickr API key this very morning and downloaded the documentation. I have to say that this kind of thing is really interesting, because it allows you to create rich mashups with a little effort. I'm not a stickler of the JSON/JavaScript approach, because I think that this kind of format should be handled using a server-side language instead of relying on a client-side support that, as many of you know, is not always available (PHP supports JSON very well, though).
As you can see, this blog integrates Flickr photos, but I don't have access to the full details of the implementation, so the best thing I can do is to write my own code and see it by myself.